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Hattori, J., R. G. Rutledge, B. L. Miki i B. R. Baum. "DNA sequence relationships and origins of acetohydroxy acid synthase genes of Brassica napus". Canadian Journal of Botany 70, nr 10 (1.10.1992): 1957–63. http://dx.doi.org/10.1139/b92-244.
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The allotetraploid Brassica napus has been shown to contain a five-member multigene family (AHAS1 – 5) of the nuclear-encoded chloroplastic enzyme acetohydroxy acid synthase, three members of which are expressed. AHAS1 and AHAS3 are constitutively expressed while AHAS2 expression is ovule- and seed-specific. By sequence and phylogenetic analyses we show that the AHAS1 and AHAS3 genes are 96–98% similar in the coding region and the adjacent 5′ and 3′ noncoding regions and were derived from a common ancestral crucifer gene. In contrast, the AHAS2 gene shares only about 80% sequence similarity with the AHAS1 and AHAS3 genes, limited to the region coding for the mature peptide and in a short region of the presumptive transit peptide. The AHAS2 gene likely arose by gene duplication of a housekeeping AHAS gene and has acquired characteristics different from other plant housekeeping AHAS genes, perhaps owing to different functional constraints. Key words: acetohydroxy acid synthase, Brassica napus, phylogenetic inference, multigene family, DNA sequence.
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Jain, Parul, i Bunyamin Tar’an. "Analysis of acetohydroxyacid synthase1 gene in chickpea conferring resistance to imazamox herbicide". Genome 57, nr 11/12 (listopad 2014): 593–600. http://dx.doi.org/10.1139/gen-2014-0145.
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Chickpea (Cicer arietinum L.) production in the Canadian prairies is challenging due to a lack of effective weed management mainly because of poor competition ability of the crop and limited registered herbicide options. Chickpea genotype with resistance to imidazolinone (IMI) herbicides has been identified. A point mutation in the acetohydroxyacid synthase1 (AHAS1) gene at C581 to T581, resulting in an amino acid substitution from Ala194 to Val194 (position 205, standardized to arabidopsis), confers the resistance to imazamox in chickpea. However, the molecular mechanism leading to the resistance is not fully understood. In many plant species, contrasting transcription levels of AHAS gene has been implicated in the resistant and susceptible genotypes in response to IMI. The objectives of this research were to compare the AHAS gene expression and AHAS enzyme activity in resistant and susceptible chickpea cultivars in response to imazamox herbicide treatment. Results from RT–qPCR indicated that there is no significant change in the transcript levels of AHAS1 between the susceptible and the resistant genotypes in response to imazamox treatment. Protein hydrophobic cluster analysis, protein-ligand docking analysis, and AHAS enzyme activity assay all indicated that the resistance to imazamox in chickpea is due to the alteration of interaction of the AHAS1 enzyme with the imazamox herbicide.
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Porat, Iris, Michael Vinogradov, Maria Vyazmensky, Chung-Dar Lu, David M. Chipman, Ahmed T. Abdelal i Ze'ev Barak. "Cloning and Characterization of Acetohydroxyacid Synthase from Bacillus stearothermophilus". Journal of Bacteriology 186, nr 2 (15.01.2004): 570–74. http://dx.doi.org/10.1128/jb.186.2.570-574.2004.
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ABSTRACT Five genes from the ilv-leu operon from Bacillus stearothermophilus have been sequenced. Acetohydroxyacid synthase (AHAS) and its subunits were separately cloned, purified, and characterized. This thermophilic enzyme resembles AHAS III of Escherichia coli, and regulatory subunits of AHAS III complement the catalytic subunit of the AHAS of B. stearothermophilus, suggesting that AHAS III is functionally and evolutionally related to the single AHAS of gram-positive bacteria.
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Fang,, Jun, Changzhao Wan, Wei Wang, Liuyin Ma, Xinqi Wang, Can Cheng, Jihua Zhou, Yongjin Qiao i Xiao Wang. "Engineering Herbicide-Tolerance Rice Expressing an Acetohydroxyacid Synthase with a Single Amino Acid Deletion". International Journal of Molecular Sciences 21, nr 4 (13.02.2020): 1265. http://dx.doi.org/10.3390/ijms21041265.
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The acetohydroxyacid synthase (AHAS) is an essential enzyme involved in branched amino acids. Several herbicides wither weeds via inhibiting AHAS activity, and the AHAS mutants show tolerance to these herbicides. However, most AHAS mutations are residue substitutions but not residue deletion. Here, residue deletion was used to engineering the AHAS gene and herbicide-tolerant rice. Molecular docking analysis predicted that the W548 of the AHAS was a residue deletion to generate herbicide tolerance. The AHAS-ΔW548 protein was generated in vitro to remove the W548 residue. Interestingly, the deletion led to the tetramer dissociation of the AHAS, while this dissociation did not reduce the activity of the AHAS. Moreover, the W548 deletion contributed to multi-family herbicides tolerance. Specially, it conferred more tolerance to sulfometuron-methyl and bispyribac-sodium than the W548L substitution. Further analysis revealed that AHAS-ΔW548 had the best performance on the sulfometuron-methyl tolerance compared to the wild-type control. Over-expression of the AHAS-ΔW548 gene into rice led to the tolerance of multiple herbicides in the transgenic line. The T-DNA insertion and the herbicide treatment did not affect the agronomic traits and yields, while more branched-chain amino acids were detected in transgenic rice seeds. Residue deletion of W548 in the AHAS could be a useful strategy for engineering herbicide tolerant rice. The increase of branched-chain amino acids might improve the umami tastes of the rice.
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Preston, Christopher, Fleur C. Dolman i Peter Boutsalis. "Multiple Resistance to Acetohydroxyacid Synthase–Inhibiting and Auxinic Herbicides in a Population of Oriental Mustard (Sisymbrium orientale)". Weed Science 61, nr 2 (czerwiec 2013): 185–92. http://dx.doi.org/10.1614/ws-d-12-00117.1.
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A population of oriental mustard from Port Broughton in South Australia was reported as not being controlled by 2,4-D. Dose response experiments determined this population was resistant to both 2,4-D and MCPA, requiring greater than 20 times more herbicide for equivalent control compared to a known susceptible population (from Roseworthy, South Australia) and a population resistant only to the acetohydroxyacid synthase (AHAS)-inhibiting herbicides (from Tumby Bay, South Australia). The Port Broughton population was also found to be resistant to three chemical groups that inhibit AHAS; however, the level of resistance was lower than the known acetolactate synthase–resistant population from Tumby Bay. Herbicides from other modes of action were able to control the Port Broughton population. Assays of isolated AHAS from the Port Broughton population showed high levels of resistance to the sulfonylurea and sulfonamide herbicide groups, but not to the imidazolinone herbicides. A single nucleotide change in the AHAS gene that predicted a Pro to Ser substitution at position 197 in the protein was identified in the Port Broughton population. This population of oriental mustard has evolved multiple resistance to AHAS-inhibiting herbicides (AHAS inhibitors) and auxinic herbicides, through a mutation in AHAS and a second nontarget-site mechanism. Whether the same mechanism provides resistance to both AHAS inhibitors and auxinic herbicides remains to be determined. Multiple resistance to auxinic herbicides and AHAS inhibitors in the Port Broughton population will make control of this population more difficult.
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Arabzadeh, Ghazaleh, i Azar Shahpiri. "Heterologous Expression and Functional Characterization of Catalytic Subunit of Rice Acetohydroxyacid Synthase". Protein & Peptide Letters 26, nr 3 (15.03.2019): 176–83. http://dx.doi.org/10.2174/0929866525666181114153727.
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Background: Acetohydroxyacid Synthase (AHAS) is the first enzyme in the biosynthesis pathway of the branched chain amino acids. AHAS is the common target site of five herbicide chemical groups: sulfonylurea, imidazolinone, triazolopyrimidine, pyrimidinyl-thiobenzoates, and sulfonyl-aminocarbonyl-triazolinone. </P><P> Objective: The purification of protein enabled us to study the physical and biochemical properties of the enzyme. In addition in vitro activity of this enzyme was tested in the presence of four different sulfonylureaherbicides and the feedback regulation of enzyme was analyzed in the presence of branched amino acids. Methods: The gene encoding catalytic subunit of rice AHAS (cOsAHAS) without part of the chloroplast transit sequence was cloned into the bacterial expression vector pET41a and heterologously expressed in Escherichia coli as carboxy-terminal extensions of glutathione-S-transferase (GST).The soluble protein was purified using affinity chromatography. The measurement of GSTOsAHAS activity was performed under optimized conditions at present of branched-chain amino acids and sulfonylurea herbicides independently. Results: The optimum pH and temperature for GST-cOsAHAS activity was 8.0 and 37 °C, respectively. The specific activity and Km value of this enzyme toward pyruvate were 0.08 U/mg and 30 mM, respectively.GST-cOsAHAS was inhibited by herbicides tribenuron, sulfosulfuron, nicosulfuron and bensulfuron while the enzyme was insensitivieto end products. Conclusion: These results suggest that the recombinant form of GST-cOsAHAS is functionally active and carries the binding site for sulfynylurea herbicides. Furthermore, GST-cOsAHAS was insensitive to feedback inhibition by endproducts which indicates the existence of a regulator subunit in rice AHAS as previously has been described in other plant AHASs.
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Singh, Vinayak, Deepak Chandra, Brahm S. Srivastava i Ranjana Srivastava. "Biochemical and transcription analysis of acetohydroxyacid synthase isoforms in Mycobacterium tuberculosis identifies these enzymes as potential targets for drug development". Microbiology 157, nr 1 (1.01.2011): 29–37. http://dx.doi.org/10.1099/mic.0.041343-0.
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Acetohydroxyacid synthase (AHAS) is a biosynthetic enzyme essential for de novo synthesis of branched-chain amino acids. The genome sequence of Mycobacterium tuberculosis revealed genes encoding four catalytic subunits, ilvB1 (Rv3003c), ilvB2 (Rv3470c), ilvG (Rv1820) and ilvX (Rv3509c), and one regulatory subunit, ilvN (Rv3002c), of AHAS. All these genes were found to be expressed in M. tuberculosis growing in vitro. Each AHAS subunit gene was cloned and expressed in Escherichia coli. AHAS activity of IlvB1 and IlvG was found in cell-free lysates and with recombinant purified proteins. Kinetic studies with purified IlvG revealed positive cooperativity towards substrate and cofactors. To understand the role of the catalytic subunits in the biology of M. tuberculosis, expression of AHAS genes was analysed in different physiological conditions. ilvB1, ilvB2 and ilvG were differentially expressed. The role of ilvB1 in persistence is known, but the upregulation of ilvB2 and ilvG in extended stationary phase, ex vivo, and in acid stress and hypoxic environments, suggests the relevance of AHAS enzymes in the metabolism and survival of M. tuberculosis by functioning as catabolic AHAS. These enzymes are therefore potential targets for drug development.
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Lonhienne, Thierry, Mario D. Garcia, Gregory Pierens, Mehdi Mobli, Amanda Nouwens i Luke W. Guddat. "Structural insights into the mechanism of inhibition of AHAS by herbicides". Proceedings of the National Academy of Sciences 115, nr 9 (13.02.2018): E1945—E1954. http://dx.doi.org/10.1073/pnas.1714392115.
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Acetohydroxyacid synthase (AHAS), the first enzyme in the branched amino acid biosynthesis pathway, is present only in plants and microorganisms, and it is the target of >50 commercial herbicides. Penoxsulam (PS), which is a highly effective broad-spectrum AHAS-inhibiting herbicide, is used extensively to control weed growth in rice crops. However, the molecular basis for its inhibition of AHAS is poorly understood. This is despite the availability of structural data for all other classes of AHAS-inhibiting herbicides. Here, crystallographic data for Saccharomyces cerevisiae AHAS (2.3 Å) and Arabidopsis thaliana AHAS (2.5 Å) in complex with PS reveal the extraordinary molecular mechanisms that underpin its inhibitory activity. The structures show that inhibition of AHAS by PS triggers expulsion of two molecules of oxygen bound in the active site, releasing them as substrates for an oxygenase side reaction of the enzyme. The structures also show that PS either stabilizes the thiamin diphosphate (ThDP)-peracetate adduct, a product of this oxygenase reaction, or traps within the active site an intact molecule of peracetate in the presence of a degraded form of ThDP: thiamine aminoethenethiol diphosphate. Kinetic analysis shows that PS inhibits AHAS by a combination of events involving FAD oxidation and chemical alteration of ThDP. With the emergence of increasing levels of resistance toward front-line herbicides and the need to optimize the use of arable land, these data suggest strategies for next generation herbicide design.
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Schwarz, Maria, Elizabeth C. Ward, Petrea Cornwell, Anne Coccetti, Pamela D'Netto, Aimee Smith i Katharine Morley-Davies. "Exploring the Validity and Operational Impact of Using Allied Health Assistants to Conduct Dysphagia Screening for Low-Risk Patients Within the Acute Hospital Setting". American Journal of Speech-Language Pathology 29, nr 4 (12.11.2020): 1944–55. http://dx.doi.org/10.1044/2020_ajslp-19-00060.
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Purpose The purpose of this study was to examine (a) the agreement between allied health assistants (AHAs) and speech-language pathologists (SLPs) when completing dysphagia screening for low-risk referrals and at-risk patients under a delegation model and (b) the operational impact of this delegation model. Method All AHAs worked in the adult acute inpatient settings across three hospitals and completed training and competency evaluation prior to conducting independent screening. Screening (pass/fail) was based on results from pre-screening exclusionary questions in combination with a water swallow test and the Eating Assessment Tool. To examine the agreement of AHAs' decision making with SLPs, AHAs ( n = 7) and SLPs ( n = 8) conducted an independent, simultaneous dysphagia screening on 51 adult inpatients classified as low-risk/at-risk referrals. To examine operational impact, AHAs independently completed screening on 48 low-risk/at-risk patients, with subsequent clinical swallow evaluation conducted by an SLP with patients who failed screening. Results Exact agreement between AHAs and SLPs on overall pass/fail screening criteria for the first 51 patients was 100%. Exact agreement for the two tools was 100% for the Eating Assessment Tool and 96% for the water swallow test. In the operational impact phase ( n = 48), 58% of patients failed AHA screening, with only 10% false positives on subjective SLP assessment and nil identified false negatives. Conclusion AHAs demonstrated the ability to reliably conduct dysphagia screening on a cohort of low-risk patients, with a low rate of false negatives. Data support high level of agreement and positive operational impact of using trained AHAs to perform dysphagia screening in low-risk patients.
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Blombach, Bastian, Stephan Hans, Brigitte Bathe i Bernhard J. Eikmanns. "Acetohydroxyacid Synthase, a Novel Target for Improvement of l-Lysine Production by Corynebacterium glutamicum". Applied and Environmental Microbiology 75, nr 2 (1.12.2008): 419–27. http://dx.doi.org/10.1128/aem.01844-08.
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ABSTRACT The influence of acetohydroxy acid synthase (AHAS) on l-lysine production by Corynebacterium glutamicum was investigated. An AHAS with a deleted C-terminal domain in the regulatory subunit IlvN was engineered by truncating the ilvN gene. Compared to the wild-type AHAS, the newly constructed enzyme showed altered kinetic properties, i.e., (i) an about twofold-lower K m for the substrate pyruvate and an about fourfold-lower V max; (ii) a slightly increased K m for the substrate α-ketobutyrate with an about twofold-lower V max; and (iii) insensitivity against the inhibitors l-valine, l-isoleucine, and l-leucine (10 mM each). Introduction of the modified AHAS into the l-lysine producers C. glutamicum DM1729 and DM1933 increased l-lysine formation by 43% (30 mM versus 21 mM) and 36% (51 mM versus 37 mM), respectively, suggesting that decreased AHAS activity is linked to increased l-lysine formation. Complete inactivation of the AHAS in C. glutamicum DM1729 and DM1933 by deletion of the ilvB gene, encoding the catalytic subunit of AHAS, led to l-valine, l-isoleucine, and l-leucine auxotrophy and to further-improved l-lysine production. In batch fermentations, C. glutamicum DM1729 ΔilvB produced about 85% more l-lysine (70 mM versus 38 mM) and showed an 85%-higher substrate-specific product yield (0.180 versus 0.098 mol C/mol C) than C. glutamicum DM1729. Comparative transcriptome analysis of C. glutamicum DM1729 and C. glutamicum DM1729 ΔilvB indicated transcriptional differences for about 50 genes, although not for those encoding enzymes involved in the l-lysine biosynthetic pathway.
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Yu, Qin, Heping Han, Martin M. Vila-Aiub i Stephen B. Powles. "AHAS herbicide resistance endowing mutations: effect on AHAS functionality and plant growth". Journal of Experimental Botany 61, nr 14 (13.07.2010): 3925–34. http://dx.doi.org/10.1093/jxb/erq205.
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Wehtje, G., i B. Brecke. "Peanut Weed Control With and Without Acetolactate Synthase-inhibiting Herbicides1". Peanut Science 31, nr 2 (1.07.2004): 113–19. http://dx.doi.org/10.3146/pnut.31.2.0010.
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Abstract Field studies were conducted in Florida and Alabama during 2001 and 2002 to compare weed control systems for peanut (Arachis hypogaea L.) that included only the herbicides registered on peanut that do not inhibit aceto hydroxyl acid synthase (AHAS). Three non-AHAS systems were identified that consistently preformed equivalent to imazapic, i.e., an AHAS-inhibiting herbicide that is very effective in peanut. These systems were either S-metolachlor plus flumioxazin, S-metolachlor plus S-dimethenamid, or S-metolachor plus norflurazon applied preemergence (PRE), followed by paraquat plus bentazon plus 2,4-DB applied postemergence. Greenhouse studies established that tank mixtures of S-metolachlor plus flumioxazin and S-metolachor plus norflurazon applied PRE were synergistic with respect to yellow nutsedge (Cyperus esculentus L.) control. This synergism may contribute to the excellent performance of these S-metolachlor-containing tank mixtures in the field. Identification of systems which utilize herbicides with modes of action other than AHAS inhibition could offer rotational alternatives to delay the emergence of AHAS-resistant weed biotypes, or alternatives should such biotypes become problematic.
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Gerwick, B. Clifford, Linda C. Mireles i Robert J. Eilers. "Rapid Diagnosis of Als/Ahas-Resistant Weeds". Weed Technology 7, nr 2 (czerwiec 1993): 519–24. http://dx.doi.org/10.1017/s0890037x00027986.
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A method to rapidly identify acetolactate synthase/acetohydroxyacid synthase (ALS/AHAS)-resistant weeds is described based upon the differential accumulation of acetoin in the presence and absence of an ALS/AHAS inhibitor herbicide. Acetoin accumulation is induced by inhibition of ketol-acid reductoisomerase (KARI), the enzyme immediately following ALS/AHAS in the biosynthesis of branched-chain amino acids. Inhibition of ALS/AHAS prevents the build up of acetoin and forms the basis for distinguishing between sensitive and resistant biotypes. A new inhibitor of KARI, 1,1-cyclopropanedicarboxylic acid (CPCA), is described and was found to cause acetoin accumulation in velvetleaf leaf disks over the concentration range of 2 to 100 000 μM. In the presence of CPCA, a number of species important to monitor for ALS/AHAS resistance were found to accumulate acetoin at rates sufficient for resistance diagnosis in 2 to 8 h. In velvetleaf, the youngest apical leaf was found to be the most active in acetoin accumulation. The resistance diagnosis method was validated by clearly distinguishing between imazaquin-sensitive and imazaquin-resistant cocklebur biotypes.
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Pearce, Claire, i Leanne Pagett. "Advanced allied health assistants: an emerging workforce". Australian Health Review 39, nr 3 (2015): 260. http://dx.doi.org/10.1071/ah14253.
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Objective Nationally and internationally there is work underway to continue to advance the scope of practice of allied health assistants (AHA). The advanced role requires additional training and competency development, as well as significant clinical experience. To build on the evidence relating to advanced scope AHAs, ACT Health undertook a project to explore the potential for the development of the local AHA workforce. This paper provides an overview of the project. Methods The potential for advanced AHAs in the Australian Capital Territory (ACT) was assessed using literature reviews, consultation with other services working with advanced AHAs and interviews with local allied health managers and assistants. Results A role for advanced AHAs within the ACT workforce was recommended, along with the need to further develop the AHA governance structure and AHA training packages and to undertake more research into the AHA workforce. Conclusion AHAs make a positive contribution to the delivery of effective, responsive, consumer-focused healthcare. The advanced AHA role provides further opportunities to enhance the flexibility of allied health services while also providing a career structure for this growing workforce.
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Kiihl, Tammy Aparecida Manabe, i Carlos Alberto Arrabal Arias. "Soybean cultivar BR-16-AHAS tolerance to the herbicide imazapyr". Pesquisa Agropecuária Brasileira 43, nr 8 (sierpień 2008): 1031–35. http://dx.doi.org/10.1590/s0100-204x2008000800012.
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The objective of this work was to evaluate the effect of the transgenic soybean BR-16-AHAS genetic constitution on the tolerance to the herbicide imazapyr. BR-16-AHAS was crossed with ten other genotypes. The experimental design was a complete randomized block, in a 2x12x3 factorial arrangement, with two sowing periods (winter and summer), twelve crossing groups and three plant positions (upper, mid and lower), with three replicates. The plants were treated with 100 g ha-1 a.i. of imazapyr at the V3/V4 stage. For each position of the plant (upper, mid and lower), the following variables were assessed: number of pods, number of seeds, seed weight, number of seeds per pod and the 100 seeds weight. The effect of the herbicide varied according to the more affected plant position (upper, mid and lower) of each genotype. The use of the same gene ahas of BR-16-AHAS, in various genotypes, results in materials with good tolerance to imazapyr; tolerance levels depend not only on the ahas gene, but also on the presence of other genes.
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Zhang, Yingying, Yang Li, Xiao Liu, Jixue Sun, Xin Li, Jianping Lin, Xue Yang, Zhen Xi i Yuequan Shen. "Molecular architecture of the acetohydroxyacid synthase holoenzyme". Biochemical Journal 477, nr 13 (2.07.2020): 2439–49. http://dx.doi.org/10.1042/bcj20200292.
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The acetohydroxyacid synthase (AHAS) holoenzyme catalyzes the first step of branch-chain amino acid biosynthesis and is essential for plants and bacteria. It consists of a regulatory subunit (RSU) and a catalytic subunit (CSU). The allosteric mechanism of the AHAS holoenzyme has remained elusive for decades. Here, we determined the crystal structure of the AHAS holoenzyme, revealing the association between the RSU and CSU in an A2B2 mode. Structural analysis in combination with mutational studies demonstrated that the RSU dimer forms extensive interactions with the CSU dimer, in which a conserved salt bridge between R32 and D120 may act as a trigger to open the activation loop of the CSU, resulting in the activation of the CSU by the RSU. Our study reveals the activation mechanism of the AHAS holoenzyme.
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KIM, Joungmok, Dong-Gil BEAK, Young-Tae KIM, Jung-Do CHOI i Moon-Young YOON. "Effects of deletions at the C-terminus of tobacco acetohydroxyacid synthase on the enzyme activity and cofactor binding". Biochemical Journal 384, nr 1 (9.11.2004): 59–68. http://dx.doi.org/10.1042/bj20040427.
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AHAS (acetohydroxyacid synthase) catalyses the first committed step in the biosynthesis of branched-chain amino acids, such as valine, leucine and isoleucine. Owing to the unique presence of these biosynthetic pathways in plants and micro-organisms, AHAS has been widely investigated as an attractive target of several classes of herbicides. Recently, the crystal structure of the catalytic subunit of yeast AHAS has been resolved at 2.8 Å (1 Å=0.1 nm), showing that the active site is located at the dimer interface and is near the herbicide-binding site. In this structure, the existence of two disordered regions, a ‘mobile loop’ and a C-terminal ‘lid’, is worth notice. Although these regions contain the residues that are known to be important in substrate specificity and in herbicide resistance, they are poorly folded into any distinct secondary structure and are not within contact distance of the cofactors. In the present study, we have tried to demonstrate the role of these regions of tobacco AHAS by constructing variants with serial deletions, based on the structure of yeast AHAS. In contrast with the wild-type AHAS, the truncated mutant which removes the C-terminal lid, Δ630, and the internal deletion mutant without the mobile loop, Δ567–582, impaired the binding affinity for ThDP (thiamine diphosphate), and showed different elution profiles representing a monomeric form in gel-filtration chromatography. Our results suggest that these regions are involved in the binding/stabilization of the active dimer and ThDP binding.
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Kutasy, Barbara, Zsolt Takács, Judit Kovács, Verëlindë Bogaj, Syafiq A. Razak, Géza Hegedűs, Kincső Decsi, Kinga Székvári i Eszter Virág. "Pro197Thr Substitution in Ahas Gene Causing Resistance to Pyroxsulam Herbicide in Rigid Ryegrass (Lolium Rigidum Gaud.)". Sustainability 13, nr 12 (10.06.2021): 6648. http://dx.doi.org/10.3390/su13126648.
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Lolium rigidum Gaud. is a cross-pollinated species characterized by high genetic diversity and it was detected as one of the most herbicide resistance-prone weeds, globally. Acetohydroxyacid synthase (AHAS) resistant populations cause significant problems in cereal production; therefore, monitoring the development of AHAS resistance is widely recommended. Using next-generation sequencing (NGS), a de novo transcriptome sequencing dataset was presented to identify the complete open reading frame (ORF) of AHAS enzyme in L. rigidum and design markers to amplify fragments consisting of all of the eight resistance-conferring amino acid mutation sites. Pro197Thr, Pro197Ala, Pro197Ser, Pro197Gln, and Trp574Leu amino acid substitutions have been observed in samples. Although the Pro197Thr amino acid substitution was already described in SU and IMI resistant populations, this is the first report to reveal that the Pro197Thr in AHAS enzyme confers a high level of resistance (ED50 3.569) to pyroxsulam herbicide (Triazolopyrimidine).
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Norazua, Zakaria, Ahmad-Hamdani Muhammad Saiful i Juraimi Abdul Shukor. "Patterns of resistance to AHAS inhibitors in Limnocharis flava from Malaysia". Plant Protection Science 54, No. 1 (24.11.2017): 48–59. http://dx.doi.org/10.17221/131/2016-pps.
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Limnocharis flava (L.) Buchenau is among the most problematic rice weeds in Malaysia and is also reported to have developed multiple resistance to AHAS inhibitor bensulfuron-methyl and synthetic auxin 2,4-D. In this study, resistance across different AHAS inhibitors was characterised in a L. flava population infesting rice fields in Pulau Pinang, Malaysia. Dose-response experiments were conducted to determine the level of resistance to sulfonylureas, imidazolinone, triazolopyrimidine, and pyrimidinyl-thiobenzoate. Cross-resistance across different AHAS inhibitors was observed in the resistant L. flava population, exhibiting a high level of resistance to bensulfuron-methyl, while exhibiting a moderate level of resistance to metsulfuron-methyl and a low level of resistance to pyrazosulfuron-ethyl and pyribenzoxim. However, all resistant L. flava individuals were still sensitive to imazethapyr, penoxsulam, and bispyribac-sodium. Based on the results, it is likely that resistance to AHAS inhibitors in L. flava is conferred by target-site resistance mechanisms.
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Shimizu, Motoyuki, Tatsuya Fujii, Shunsuke Masuo i Naoki Takaya. "Mechanism of De Novo Branched-Chain Amino Acid Synthesis as an Alternative Electron Sink in Hypoxic Aspergillus nidulans Cells". Applied and Environmental Microbiology 76, nr 5 (15.01.2010): 1507–15. http://dx.doi.org/10.1128/aem.02135-09.
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ABSTRACT Although branched-chain amino acids are synthesized as building blocks of proteins, we found that the fungus Aspergillus nidulans excretes them into the culture medium under hypoxia. The transcription of predicted genes for synthesizing branched-chain amino acids was upregulated by hypoxia. A knockout strain of the gene encoding the large subunit of acetohydroxy acid synthase (AHAS), which catalyzes the initial reaction of the synthesis, required branched-chain amino acids for growth and excreted very little of them. Pyruvate, a substrate for AHAS, increased the amount of hypoxic excretion in the wild-type strain. These results indicated that the fungus responds to hypoxia by synthesizing branched-chain amino acids via a de novo mechanism. We also found that the small subunit of AHAS regulated hypoxic branched-chain amino acid production as well as cellular AHAS activity. The AHAS knockout resulted in higher ratios of NADH/NAD+ and NADPH/NADP+ under hypoxia, indicating that the branched-chain amino acid synthesis contributed to NAD+ and NADP+ regeneration. The production of branched-chain amino acids and the hypoxic induction of involved genes were partly repressed in the presence of glucose, where cells produced ethanol and lactate and increased levels of lactate dehydrogenase activity. These indicated that hypoxic branched-chain amino acid synthesis is a unique alternative mechanism that functions in the absence of glucose-to-ethanol/lactate fermentation and oxygen respiration.
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Boigegrain, Rose-Anne, Jean-Pierre Liautard i Stephan Köhler. "Targeting of the Virulence Factor Acetohydroxyacid Synthase by Sulfonylureas Results in Inhibition of Intramacrophagic Multiplication of Brucella suis". Antimicrobial Agents and Chemotherapy 49, nr 9 (wrzesień 2005): 3922–25. http://dx.doi.org/10.1128/aac.49.9.3922-3925.2005.
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ABSTRACT The acetohydroxyacid synthase (AHAS) of Brucella suis can be effectively targeted by the sulfonylureas chlorimuron ethyl and metsulfuron methyl. Growth in minimal medium was inhibited, and multiplication in human macrophages was totally abolished with 100 μM of sulfonylureas. Metsulfuron methyl-resistant mutants showed reduced viability in macrophages and reduced AHAS activity.
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Garcia, Mario D., Amanda Nouwens, Thierry G. Lonhienne i Luke W. Guddat. "Comprehensive understanding of acetohydroxyacid synthase inhibition by different herbicide families". Proceedings of the National Academy of Sciences 114, nr 7 (30.01.2017): E1091—E1100. http://dx.doi.org/10.1073/pnas.1616142114.
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Five commercial herbicide families inhibit acetohydroxyacid synthase (AHAS, E.C. 2.2.1.6), which is the first enzyme in the branched-chain amino acid biosynthesis pathway. The popularity of these herbicides is due to their low application rates, high crop vs. weed selectivity, and low toxicity in animals. Here, we have determined the crystal structures of Arabidopsis thaliana AHAS in complex with two members of the pyrimidinyl-benzoate (PYB) and two members of the sulfonylamino-carbonyl-triazolinone (SCT) herbicide families, revealing the structural basis for their inhibitory activity. Bispyribac, a member of the PYBs, possesses three aromatic rings and these adopt a twisted “S”-shaped conformation when bound to A. thaliana AHAS (AtAHAS) with the pyrimidinyl group inserted deepest into the herbicide binding site. The SCTs bind such that the triazolinone ring is inserted deepest into the herbicide binding site. Both compound classes fill the channel that leads to the active site, thus preventing substrate binding. The crystal structures and mass spectrometry also show that when these herbicides bind, thiamine diphosphate (ThDP) is modified. When the PYBs bind, the thiazolium ring is cleaved, but when the SCTs bind, ThDP is modified to thiamine 2-thiazolone diphosphate. Kinetic studies show that these compounds not only trigger reversible accumulative inhibition of AHAS, but also can induce inhibition linked with ThDP degradation. Here, we describe the features that contribute to the extraordinarily powerful herbicidal activity exhibited by four classes of AHAS inhibitors.
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Epelbaum, Sabine, Robert A. LaRossa, Tina K. VanDyk, T. Elkayam, David M. Chipman i Ze’ev Barak. "Branched-Chain Amino Acid Biosynthesis in Salmonella typhimurium: a Quantitative Analysis". Journal of Bacteriology 180, nr 16 (15.08.1998): 4056–67. http://dx.doi.org/10.1128/jb.180.16.4056-4067.1998.
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ABSTRACT We report here the first quantitative study of the branched-chain amino acid biosynthetic pathway in Salmonella typhimurium LT2. The intracellular levels of the enzymes of the pathway and of the 2-keto acid intermediates were determined under various physiological conditions and used for estimation of several of the fluxes in the cells. The results led to a revision of previous ideas concerning the way in which multiple acetohydroxy acid synthase (AHAS) isozymes contribute to the fitness of enterobacteria. In wild-type LT2, AHAS isozyme I provides most of the flux to valine, leucine, and pantothenate, while isozyme II provides most of the flux to isoleucine. With acetate as a carbon source, a strain expressing AHAS II only is limited in growth because of the low enzyme activity in the presence of elevated levels of the inhibitor glyoxylate. A strain with AHAS I only is limited during growth on glucose by the low tendency of this enzyme to utilize 2-ketobutyrate as a substrate; isoleucine limitation then leads to elevated threonine deaminase activity and an increased 2-ketobutyrate/2-ketoisovalerate ratio, which in turn interferes with the synthesis of coenzyme A and methionine. The regulation of threonine deaminase is also crucial in this regard. It is conceivable that, because of fundamental limitations on the specificity of enzymes, no single AHAS could possibly be adequate for the varied conditions that enterobacteria successfully encounter.
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Lee, Yu-Ting, i Ronald G. Duggleby. "Mutations in the regulatory subunit of yeast acetohydroxyacid synthase affect its activation by MgATP". Biochemical Journal 395, nr 2 (28.03.2006): 331–36. http://dx.doi.org/10.1042/bj20051793.
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Isoleucine, leucine and valine are synthesized via a common pathway in which the first reaction is catalysed by AHAS (acetohydroxyacid synthase; EC 2.2.1.6). This heterotetrameric enzyme is composed of a larger subunit that contains the catalytic machinery and a smaller subunit that plays a regulatory role. The RSU (regulatory subunit) enhances the activity of the CSU (catalytic subunit) and mediates end-product inhibition by one or more of the branched-chain amino acids, usually valine. Fungal AHAS differs from that in other organisms in that the inhibition by valine is reversed by MgATP. The fungal AHAS RSU also differs from that in other organisms in that it contains a sequence insert. We suggest that this insert may form the MgATP-binding site and we have tested this hypothesis by mutating ten highly conserved amino acid residues of the yeast AHAS RSU. The modified subunits were tested for their ability to activate the yeast AHAS CSU, to confer sensitivity to valine inhibition and to mediate reversal of the inhibition by MgATP. All but one of the mutations resulted in substantial changes in the properties of the RSU. Unexpectedly, four of them gave a protein that required MgATP in order for strong stimulation of the CSU and valine inhibition to be observed. A model to explain this result is proposed. Five of the mutations abolished MgATP activation and are suggested to constitute the binding site for this modulator.
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Awasthy, Disha, Sheshagiri Gaonkar, R. K. Shandil, Reena Yadav, Sowmya Bharath, Nimi Marcel, Venkita Subbulakshmi i Umender Sharma. "Inactivation of the ilvB1 gene in Mycobacterium tuberculosis leads to branched-chain amino acid auxotrophy and attenuation of virulence in mice". Microbiology 155, nr 9 (1.09.2009): 2978–87. http://dx.doi.org/10.1099/mic.0.029884-0.
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Acetohydroxyacid synthase (AHAS) is the first enzyme in the branched-chain amino acid biosynthesis pathway in bacteria. Bioinformatics analysis revealed that the Mycobacterium tuberculosis genome contains four genes (ilvB1, ilvB2, ilvG and ilvX) coding for the large catalytic subunit of AHAS, whereas only one gene (ilvN or ilvH) coding for the smaller regulatory subunit of this enzyme was found. In order to understand the physiological role of AHAS in survival of the organism in vitro and in vivo, we inactivated the ilvB1 gene of M. tuberculosis. The mutant strain was found to be auxotrophic for all of the three branched-chain amino acids (isoleucine, leucine and valine), when grown with either C6 or C2 carbon sources, suggesting that the ilvB1 gene product is the major AHAS in M. tuberculosis. Depletion of these branched chain amino acids in the medium led to loss of viability of the ΔilvB1 strain in vitro, resulting in a 4-log reduction in colony-forming units after 10 days. Survival kinetics of the mutant strain cultured in macrophages maintained with sub-optimal concentrations of the branched-chain amino acids did not show any loss of viability, indicating either that the intracellular environment was rich in these amino acids or that the other AHAS catalytic subunits were functional under these conditions. Furthermore, the growth kinetics of the ΔilvB1 strain in mice indicated that although this mutant strain showed defective growth in vivo, it could persist in the infected mice for a long time, and therefore could be a potential vaccine candidate.
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JUNG, Sun-Mi, Dung Tien LE, Sung-Sook YOON, Moon-Young YOON, Young Tae KIM i Jung-Do CHOI. "Amino acid residues conferring herbicide resistance in tobacco acetohydroxy acid synthase". Biochemical Journal 383, nr 1 (24.09.2004): 53–61. http://dx.doi.org/10.1042/bj20040720.
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The enzyme AHAS (acetohydroxy acid synthase), which is involved in the biosynthesis of valine, leucine and isoleucine, is the target of several classes of herbicides. A model of tobacco AHAS was generated based on the X-ray structure of yeast AHAS. Well conserved residues at the herbicide-binding site were identified, and the roles of three of these residues (Phe-205, Val-570 and Phe-577) were determined by site-directed mutagenesis. The Phe-205 mutants F205A, F205H, F205W and F205Y showed markedly decreased levels of catalytic efficiency, and cross-resistance to two or three classes of herbicides, i.e. Londax (a sulphonylurea herbicide), Cadre (an imidazolinone herbicide) and TP (a triazolopyrimidine derivative). None of the mutations caused significant changes in the secondary or tertiary structure of the enzyme. Four mutants of Phe-577, i.e. F577D, F577E, F577K and F577R, showed unaltered Vmax values, but substantially decreased catalytic efficiency. However, these mutants were highly resistant to two or three of the tested herbicides. The three mutants F577D, F577E and F577R had a similar secondary structure to that of wild-type AHAS. Conservative mutations of Phe-577, i.e. F577W and F577Y, did not affect the kinetic properties of the enzyme or its inhibition by herbicides. The mutation Val-570 to Asn abolished the binding affinity of the enzyme for FAD as well as its activity, and also caused a change in the tertiary structure of AHAS. However, the mutant V570Q was active, but resistant to two classes of herbicides, i.e. Londax and TP. The conservative mutant V570I was substantially reduced in catalytic efficiency and moderately resistant to the three herbicides. The results of this study suggest that residues Phe-205, Val-570 and Phe-577 in tobacco AHAS are located at or near the binding site that is common for the three classes of herbicides. In addition, Phe-205 and Val-570 are probably located at the herbicide-binding site that may overlap partially with the active site. Selected mutants of Phe-577 are expected to be utilized to construct herbicide-resistant transgenic plants.
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Kreisberg, Jason F., Nicholas T. Ong, Aishwarya Krishna, Thomas L. Joseph, Jing Wang, Catherine Ong, Hui Ann Ooi i in. "Growth Inhibition of Pathogenic Bacteria by Sulfonylurea Herbicides". Antimicrobial Agents and Chemotherapy 57, nr 3 (21.12.2012): 1513–17. http://dx.doi.org/10.1128/aac.02327-12.
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ABSTRACTEmerging resistance to current antibiotics raises the need for new microbial drug targets. We show that targeting branched-chain amino acid (BCAA) biosynthesis using sulfonylurea herbicides, which inhibit the BCAA biosynthetic enzyme acetohydroxyacid synthase (AHAS), can exert bacteriostatic effects on several pathogenic bacteria, includingBurkholderia pseudomallei,Pseudomonas aeruginosa, andAcinetobacter baumannii. Our results suggest that targeting biosynthetic enzymes like AHAS, which are lacking in humans, could represent a promising antimicrobial drug strategy.
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Caforio, Alida L. P., Anna Baritussio, Renzo Marcolongo, Chun-Yan Cheng, Elena Pontara, Elisa Bison, Maria Grazia Cattini i in. "Serum Anti-Heart and Anti-Intercalated Disk Autoantibodies: Novel Autoimmune Markers in Cardiac Sarcoidosis". Journal of Clinical Medicine 10, nr 11 (2.06.2021): 2476. http://dx.doi.org/10.3390/jcm10112476.
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Background: Sarcoidosis is an immune-mediated disease. Cardiac involvement, a granulomatous form of myocarditis, is under-recognized and prognostically relevant. Anti-heart autoantibodies (AHAs) and anti-intercalated disk autoantibodies (AIDAs) are autoimmune markers in nonsarcoidosis myocarditis forms. Objective: The aim was to assess serum AHAs and AIDAs as autoimmune markers in cardiac sarcoidosis. Methods: This is a cross-sectional study on AHA and AIDA frequency in: 29 patients (aged 46 ± 12, 20 male) with biopsy-proven extracardiac sarcoidosis and biopsy-proven or clinically suspected and confirmed by 18-fluorodeoxyglucose positron emission tomography and/or cardiovascular magnetic resonance (CMR) cardiac involvement; 30 patients (aged 44 ± 11, 12 male) with biopsy-proven extracardiac sarcoidosis without cardiac involvement (no cardiac symptoms, normal 12-lead electrocardiogram, echocardiography and CMR), and control patients with noninflammatory cardiac disease (NICD) (n = 160), ischemic heart failure (IHF) (n = 141) and normal blood donors (NBDs) (n = 270). Sarcoidosis patients were recruited in two recruiting tertiary centers in the USA and Italy. AHAs and AIDAs were detected by indirect immunofluorescence on the human myocardium and skeletal muscle. Results: AHA and AIDA frequencies were higher in sarcoidosis with cardiac involvement (86%; 62%) than in sarcoidosis without cardiac involvement (0%; 0%), NICD (8%; 4%), IHF (7%; 2%) and NBD (9%; 0%) (p = 0.0001; p = 0.0001, respectively). Sensitivity and specificity for cardiac sarcoidosis were 86% and 92% for positive AHAs and 62% and 98% for positive AIDAs, respectively. AIDAs in cardiac sarcoidosis were associated with a higher number of involved organs (p = 0.04). Conclusions: Serum AHAs and AIDAs provide novel noninvasive diagnostic autoimmune markers for cardiac sarcoidosis.
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Slishchuk, H. I., N. E. Volkova, O. O. Zakharova i A. V. Korchmaryоvа. "Bioinformatic analysis of chickpea acetohydroxyacid synthase gene". Faktori eksperimental'noi evolucii organizmiv 24 (30.08.2019): 345–49. http://dx.doi.org/10.7124/feeo.v24.1127.
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Aim. Analysis of homologues of chickpea gene encoding acetohydroxyacid synthase, by bioinformatics methods. Methods. Alignment of nucleotide sequences, UPGMA method, Maximum Composite Likelihood method, homologous modeling of three-dimensional structure of enzyme. Results. Homologues of the acetohydroxyacid syntase gene (AHAS) of chickpea were found among representatives of different families. A certain level of conservativeness of mRNA homologues sequences of AHAS gene within the families was noted, including legumes. The distribution of clusters corresponds to the taxonomic position of the investigated plant species. The single nucleotide polymorphism C / T at position 581, potentially associated with herbicide resistance, was detected. Based on the homologous modeling results, two models of the enzyme AHAS were constructed. The replacement of C / T, which leads to the replacement of the amino acids of alanine with valine, leads to a change in the conformation in the A chain of protein. Conclusions. Marker screening of the source breeding material by «real-time» polymerase chain reaction with the developed primers and the TaqMan probe to the polymorphic region of the AHAS gene will allow differentiating the herbicide «resistant» and «tolerant» alleles of the gene for the selection of target genotypes.
Keywords: chickpea, acetohydroxyacid syntase gene, single nucleotide polymorphism, resistance to herbicides.
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Garcia, Mario D., Sheena M. H. Chua, Yu-Shang Low, Yu-Ting Lee, Kylie Agnew-Francis, Jian-Guo Wang, Amanda Nouwens i in. "Commercial AHAS-inhibiting herbicides are promising drug leads for the treatment of human fungal pathogenic infections". Proceedings of the National Academy of Sciences 115, nr 41 (24.09.2018): E9649—E9658. http://dx.doi.org/10.1073/pnas.1809422115.
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The increased prevalence of drug-resistant human pathogenic fungal diseases poses a major threat to global human health. Thus, new drugs are urgently required to combat these infections. Here, we demonstrate that acetohydroxyacid synthase (AHAS), the first enzyme in the branched-chain amino acid biosynthesis pathway, is a promising new target for antifungal drug discovery. First, we show that several AHAS inhibitors developed as commercial herbicides are powerful accumulative inhibitors of Candida albicans AHAS (Ki values as low as 800 pM) and have determined high-resolution crystal structures of this enzyme in complex with several of these herbicides. In addition, we have demonstrated that chlorimuron ethyl (CE), a member of the sulfonylurea herbicide family, has potent antifungal activity against five different Candida species and Cryptococcus neoformans (with minimum inhibitory concentration, 50% values as low as 7 nM). Furthermore, in these assays, we have shown CE and itraconazole (a P450 inhibitor) can act synergistically to further improve potency. Finally, we show in Candida albicans-infected mice that CE is highly effective in clearing pathogenic fungal burden in the lungs, liver, and spleen, thus reducing overall mortality rates. Therefore, in view of their low toxicity to human cells, AHAS inhibitors represent a new class of antifungal drug candidates.
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Dutton, Tegan, Wendy Stevens i Jamie Newman. "Health assessments for Indigenous Australians at Orange Aboriginal Medical Service: health problems identified and subsequent follow up". Australian Journal of Primary Health 22, nr 3 (2016): 233. http://dx.doi.org/10.1071/py14120.
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This study aimed to document the types, management and follow up of health issues identified by all Aboriginal Health Assessments (AHA) performed at Orange Aboriginal Medical Service from 1 January 2011 to 31 December 2012. This was done with a retrospective audit of clinical records. In total, 1169 AHAs were performed: 41% child, 53% adult and 6% older person AHAs. Newly identified health issues were documented in 85% (984). Being overweight (41%; 476) and smoking (26%; 301) were the common risk factors identified. As a result of the AHA, most children who were not up-to-date with their vaccinations received catch-up immunisations; 11% (36) of adult women (n=314) received a Pap smear, although Pap smear status was unknown or not up-to-date for 61% (192); 27% (311) of cases were prescribed new medication; and 1239 referrals were made but only 40% were attended. At 6 months following the AHA, 26% (240) of cases with newly identified health issues were completely managed and followed up, whereas 25% (226) received no follow up. The AHAs are useful for identifying new health issues; however, follow up of the identified health issues should be improved. If AHAs are to improve health outcomes, appropriate management and follow up of the identified health issues are essential.
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Jackson, Edward M. "Ahas: What's Wrong with This Picture?" Journal of Toxicology: Cutaneous and Ocular Toxicology 16, nr 4 (styczeń 1997): 203–5. http://dx.doi.org/10.3109/15569529709048898.
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HILL, Craig M., i Ronald G. DUGGLEBY. "Mutagenesis of Escherichia coli acetohydroxyacid synthase isoenzyme II and characterization of three herbicide-insensitive forms". Biochemical Journal 335, nr 3 (1.11.1998): 653–61. http://dx.doi.org/10.1042/bj3350653.
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Sulphonylurea and imidazolinone herbicides act by inhibiting acetohydroxyacid synthase (AHAS; EC 4.1.3.18), the enzyme that catalyses the first step in the biosynthesis of branched-chain amino acids. AHAS requires as cofactors thiamin diphosphate, a bivalent metal ion and, usually, FAD. Escherichia coli contains three isoenzymes and this study concerns isoenzyme II, the most herbicide-sensitive of the E. coli forms. A plasmid containing the large and small subunit genes of AHAS II was mutagenized using hydroxylamine and clones resistant to the sulphonylurea chlorimuron ethyl were selected. Three mutants were isolated; A26V, V99M and A108V. A26V has been described previously whereas the equivalent mutation of A108V has been reported in a herbicide-insensitive variant of yeast AHAS. The V99M mutation has not been discovered previously in AHAS from any source. The mutants were each over-expressed in E. coli, and the enzymes were purified to homogeneity. Some differences from wild type in the kinetic properties (kcat, Km and cofactor affinities) were observed, most notably a 28-fold decrease in the affinity for thiamin diphosphate of V99M. None of the mutants shows marked changes from the wild type in sensitivity to three imidazolinones, with the largest increase in the apparent inhibition constant being a factor of approximately 5. The A26V mutant is weakly resistant (6- to 20-fold) to six sulphonylureas, whereas stronger resistance is seen in V99M (20- to 250-fold) and A108V (35- to 420-fold). Resistance as a result of these mutations is consistent with a molecular model of the herbicide-binding site, which predicts that mutation of G249 might also confer herbicide insensitivity. Three G249 mutants were constructed, expressed and purified but all are inactive, apparently because they cannot bind FAD.
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Hernández, María J., Rocío León, Albert J. Fischer, Marlene Gebauer, Rafael Galdames i Rodrigo Figueroa. "Target-Site Resistance to Nicosulfuron in Johnsongrass (Sorghum halepense) from Chilean Corn Fields". Weed Science 63, nr 3 (wrzesień 2015): 631–40. http://dx.doi.org/10.1614/ws-d-14-00167.1.
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Johnsongrass is a common weed of corn in Chile, which is most often controlled by nicosulfuron, an acetohydroxyacid synthase (AHAS)-inhibiting herbicide. Recurrent nicosulfuron use has resulted in selection for resistant johnsongrass biotypes. We conducted studies to determine nicosulfuron resistance levels in two johnsongrass biotypes from Chile and to investigate if this resistance was target-site mediated. Whole-plant resistance to nicosulfuron was 33 and 46 times higher in resistant (R) than in susceptible (S) plants grown from seed and rhizomes, respectively. The nicosulfuron concentrations for 50% inhibition of AHAS enzyme activity in vitro were more than 11 times higher in R than in S plants. Sequencing analysis of theAHAScoding sequence revealed a Trp-574-Leu substitution in both R biotypes. This study shows that resistance to nicosulfuron in the two R biotypes is conferred by an altered target site. We also report the first consensus sequence of the johnsongrassAHASgene corresponding to the known mutation sites conferring resistance to AHAS-inhibiting herbicides.
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ElišÃ¯Â¿Â½kov�, Veronika, Miroslav P�tek, Jiř� Hol�tko, Jan Nešvera, Damien Leyval, Jean-Louis Goergen i St�phane Delaunay. "Feedback-Resistant Acetohydroxy Acid Synthase Increases Valine Production in Corynebacterium glutamicum". Applied and Environmental Microbiology 71, nr 1 (styczeń 2005): 207–13. http://dx.doi.org/10.1128/aem.71.1.207-213.2005.
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ABSTRACT Acetohydroxy acid synthase (AHAS), which catalyzes the key reactions in the biosynthesis pathways of branched-chain amino acids (valine, isoleucine, and leucine), is regulated by the end products of these pathways. The whole Corynebacterium glutamicum ilvBNC operon, coding for acetohydroxy acid synthase (ilvBN) and aceto hydroxy acid isomeroreductase (ilvC), was cloned in the newly constructed Escherichia coli-C. glutamicum shuttle vector pECKA (5.4 kb, Kmr). By using site-directed mutagenesis, one to three amino acid alterations (mutations M8, M11, and M13) were introduced into the small (regulatory) AHAS subunit encoded by ilvN. The activity of AHAS and its inhibition by valine, isoleucine, and leucine were measured in strains carrying the ilvBNC operon with mutations on the plasmid or the ilvNM13 mutation within the chromosome. The enzyme containing the M13 mutation was feedback resistant to all three amino acids. Different combinations of branched-chain amino acids did not inhibit wild-type AHAS to a greater extent than was measured in the presence of 5 mM valine alone (about 57%). We infer from these results that there is a single binding (allosteric) site for all three amino acids in the enzyme molecule. The strains carrying the ilvNM13 mutation in the chromosome produced more valine than their wild-type counterparts. The plasmid-free C. glutamicum ΔilvA ΔpanB ilvNM13 strain formed 90 mM valine within 48 h of cultivation in minimal medium. The same strain harboring the plasmid pECKAilvBNC produced as much as 130 mM valine under the same conditions.
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Ashigh, Jamshid, i François J. Tardif. "An Ala205Val Substitution in Acetohydroxyacid Synthase of Eastern Black Nightshade (Solanum ptychanthum) Reduces Sensitivity to Herbicides and Feedback Inhibition". Weed Science 55, nr 6 (grudzień 2007): 558–65. http://dx.doi.org/10.1614/ws-07-054.1.
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Twelve populations of eastern black nightshade from different locations in Ontario are resistant to imazethapyr. This study aimed at determining the molecular basis of resistance in these populations and the activity of the resistant acetohydroxyacid synthase (AHAS) enzyme compared to that of the sensitive AHAS in response to different herbicides and branched-chain amino acid concentration. The results of partialAHASsequencing indicated that all resistant populations had a cytosine331to thymine substitution coding for an alanine205to valine substitution.In vitroAHAS enzyme assays of one resistant population showed that the specific activity of the resistant enzyme was 56% less than that of the susceptible enzyme. AHAS from the resistant population was 72-, 70-, and 64-fold less sensitive than that of the susceptible population to imazethapyr, imazamox, and primisulfuron, respectively. Furthermore, the resistant enzyme was less sensitive to feedback inhibition from branched-chain amino acids compared to the susceptible enzyme. Results confirmed that resistance in resistant populations of eastern black nightshade was conferred by target-site modification and that the Ala205Val substitution alters the kinetics and regulation of branched-chain amino acid biosynthesis.
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Tanriverdi, Fatih, Annamaria De Bellis, Marina Battaglia, Giuseppe Bellastella, Antonio Bizzarro, Antonio A. Sinisi, Antonio Bellastella i in. "Investigation of antihypothalamus and antipituitary antibodies in amateur boxers: is chronic repetitive head trauma-induced pituitary dysfunction associated with autoimmunity?" European Journal of Endocrinology 162, nr 5 (maj 2010): 861–67. http://dx.doi.org/10.1530/eje-09-1024.
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ObjectiveCurrent data clearly demonstrate that sports-related chronic repetitive head trauma due to boxing might result in hypopituitarism. However, the mechanism of sports-related traumatic brain injury-induced pituitary dysfunction is still unclear. In order to understand whether autoimmune mechanisms could play a role in the pituitary dysfunction due to sports-related head trauma, we investigated the presence of antipituitary antibodies (APAs) and antihypothalamus antibodies (AHAs) in amateur boxers.Patients and designSixty-one actively competing (n=44) or retired (n=17) male boxers (mean age, 26 years; range, 17–53) who had been evaluated regarding pituitary functions previously were included in the study. In all boxers and in 60 age/sex-similar normal controls, AHAs and APAs were investigated by an indirect immunofluorescence method.ResultsAHAs were detected in 13 of 61 boxers (21.3%), and APAs were detected in 14 of 61 boxers (22.9%), but in none of the normal controls. Pituitary dysfunction was significantly higher in AHA-positive boxers (46.2%) than in AHA-negative boxers (10.4%) (P=0.003). There was a significant association between AHA positivity and hypopituitarism due to boxing (odds ratio: 7.37, 95% confidence interval 1.8–30.8). There was no significant association between APA positivity and hypopituitarism.ConclusionsThis study demonstrates for the first time the presence of AHAs and APAs in boxers who were exposed to sports-related head trauma. Moreover, the present investigation provides preliminary evidence that AHAs are associated with the development of pituitary dysfunction in boxers, thus suggesting that autoimmunity may have a role in the pathogenesis.
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Ilana Rubenfeld, Ph.D. "The Rubenfeld Synergy Method: The Six “Ahas”". Gestalt Review 4, nr 4 (2000): 319. http://dx.doi.org/10.5325/gestaltreview.4.4.0319.
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Gartner, Georg. "In Memoriam: Professor Rein Ahas (1966–2018)". Journal of Location Based Services 12, nr 1 (2.01.2018): 1. http://dx.doi.org/10.1080/17489725.2018.1470862.
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Yu, Qin, i Stephen B. Powles. "Resistance to AHAS inhibitor herbicides: current understanding". Pest Management Science 70, nr 9 (20.01.2014): 1340–50. http://dx.doi.org/10.1002/ps.3710.
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Andersen, F. A. "Final Report On the Safety Assessment of Glycolic Acid, Ammonium, Calcium, Potassium, and Sodium Glycolates, Methyl, Ethyl, Propyl, and Butyl Glycolates, and Lactic Acid, Ammonium, Calcium, Potassium, Sodium, and Tea-Lactates, Methyl, Ethyl, Isopropyl, and Butyl Lactates, and Lauryl, Myristyl, and Cetyl Lactates". International Journal of Toxicology 17, nr 1_suppl (styczeń 1998): 1–241. http://dx.doi.org/10.1177/109158189801700101.
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This report provides a review of the safety of Glycolic Acid, Ammonium, Calcium, Potassium, and Sodium Glycolates, Methyl, Ethyl, Propyl, and Butyl Glycolates, Lactic Acid, Ammonium, Calcium, Potassium, Sodium, and TEA-Lactates, and Lauryl, Myristyl, and Cetyl Lactates. These ingredients belong to a group known as alpha-hydroxy acids (AHAs). Products containing these ingredients may be for consumer use, salon use, or medical use. This report does not address the medical use. In consumer and salon use, AHAs can function as mild exfoliants, but are also used as pH adjusters and skin-conditioning agents. AHAs are absorbed by the skin; the lower the pH, the greater the absorption. Metabolism and distribution studies show expected pathways and distribution. Consistent with these data, acute oral animal studies show oxalate-induced renal calculi, an increase in renal oxalate, and nephrotoxic effects. No systemic effects in animals were seen with dermal application, but irritation at the sight of application was produced. While many animal studies were performed to evaluate AHA-induced skin irritation, it was common for either the AHA concentration or the pH of the formulation to be omitted, limiting the usefulness of the data. Clinical testing using AHA formulations of known concentration and pH was done to address the issue of skin irritation as a function of concentration and pH. Skin irritation increased with AHA concentration at a given pH. Skin irritation increased when the pH of a given AHA concentration was lowered. Repeat insult patch tests using lotions and creams containing up to 10% Glycolic or Lactic Acid were negative. Glycolic Acid at concentrations up to 10% was not comedogenic and Lactic Acid at the same concentrations did not cause immediate urticarial reactions. Glycolic Acid was found to be nonirritating to minimally irritating in animal ocular tests, while Lactic Acid was found to be nonirritating to moderately irritating. In vitro testing to predict ocular irritation suggested Glycolic Acid would be a minimal to moderate-severe ocular irritant, and that Lactic Acid would be a minimal to moderate ocular irritant. Developmental and maternal toxicity were reported in rats dosed by gavage at the highest dose level used in a study that exposed the animals on days 7-21 of gestation. No developmental toxicity was reported at levels that were not maternally toxic. AHAs were almost uniformly negative in genotoxicity tests and were not carcinogenic in rabbits or rats. Clinical reports suggested that AHAs would enhance the penetration of hydroquinone and lidocaine. Animal and clinical tests were done to further evaluate the potential ofAHAs to enhance the skin penetration of other chemical agents. Pretreatment of guinea pig skin with Glycolic Acid did not affect the absorption of hydroquinone or musk xylol. Clinical tests results indicated no increase in penetration of hydrocortisone or glycerin with Glycolic Acid pretreatment. Because AHAs can act to remove a portion of the stratum corneum, concern was expressed about the potential that pretreatment with AHAs could increase skin damage produced by UV radiation. Clinical testing was done to determine the number of sunburn cells (cells damaged by UV radiation that show distinct morphologic changes) produced by 1 MED of UV radiation in skin pretreated with AHAs. A statistically significant increase in the number of sunburn cells was seen in skin pretreated with AHAs compared to controls. These increases, however, were less than those seen when the UV dose was increased from 1 MED to 1.56 MED. The increase in UV radiation damage associated with AHA pretreatment, therefore, was of such a magnitude that it is easily conceivable that aspects of product formulation could eliminate the effect. Based on the available information included in this report, the CIR Expert Panel concluded that Glycolic and Lactic Acid, their common salts and their simple esters, are safe for use in cosmetic products at concentrations ≤10%, at final formulation pH≥3.5, when formulated to avoid increasing sun sensitivity or when directions for use include the daily use of sun protection. These ingredients are safe for use in salon products at concentrations ≤30%, at final formulation pH ≥3.0, in products designed for brief, discontinuous use followed by thorough rinsing from the skin, when applied by trained professionals, and when application is accompanied by directions for the daily use of sun protection.
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Rubin, Baruch, i John E. Casida. "R-25788 Effects on Chlorsulfuron Injury and Acetohydroxyacid Synthase Activity". Weed Science 33, nr 4 (lipiec 1985): 462–68. http://dx.doi.org/10.1017/s0043174500082667.
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Chlorsulfuron {2-chloro-N-[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)amino] carbonyl]-benzenesulfonamide} applied preemergence or postemergence as a soil drench retards the growth of four corn (Zea maysL.) genotypes in soil with 50% inhibition in each case at a rate of approximately 5 g ai/ha. R-25788 (N,N-diallyl-2,2-dichloroacetamide), applied at 1.0 kg ai/ha to the soil preemergence with chlorsulfuron or postemergence 2 days prior to chlorsulfuron treatment, reverses shoot growth inhibition induced by the herbicide in varying degree in ‘XL25A’ and ‘XL72B’ corn hybrids and ‘FRM017’ and ‘FR619’ inbreds, but not in soybean [Glycine max(L.) Merr., var. ‘Amsoy-71’]. Under similar conditions, flurazole [2-chloro-4-(trifluoromethyl)-5-thiazolecarboxylic acid (phenylmethyl ester)] and CGA-92194 [α-(1,3-dioxolan-2-yl-methoxy)-imino-benzeneacetonitrile] are less effective than R-25788 in protecting corn genotypes from chlorsulfuron injury. R-25788 also partially reverses chlorsulfuron-induced root growth inhibition in XL25A and FR619 corn but not in pea (Pisum sativumL. var. ‘Dwarf Gray Sugar’). Acetohydroxyacid synthase (AHAS) is higher in both activity and the proportion that is very sensitive to in vitro chlorsulfuron inhibition when prepared from XL25A shoots than from the roots. R-25788 does not reverse the in vitro inhibition of corn acetohydroxyacid synthase (AHAS) by chlorsulfuron. Pretreatment of 5-day-old XL25A corn with R-25788 at 24 or 48 μM significantly increases AHAS activity by approximately 25% in both shoots and roots but does not change its in vitro sensitivity to chlorsulfuron. This antidote also increases the glutathione (GSH) content in roots and etiolated shoots. The R-25788-induced elevation of AHAS activity may contribute to its antidotal effect in corn.
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Somerville, Lisa, Annette Davis, Andrea L. Elliott, Desiree Terrill, Nicole Austin i Kathleen Philip. "Building allied health workforce capacity: a strategic approach to workforce innovation". Australian Health Review 39, nr 3 (2015): 264. http://dx.doi.org/10.1071/ah14211.
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Objective The aim of the present study was to identify areas where allied health assistants (AHAs) are not working to their full scope of practice in order to improve the effectiveness of the allied health workforce. Methods Qualitative data collected via focus groups identified suitable AHA tasks and a quantitative survey with allied health professionals (AHPs) measured the magnitude of work the current AHP workforce spends undertaking these tasks. Results Quantification survey results indicate that Victoria’s AHP workforce spends up to 17% of time undertaking tasks that could be delegated to an AHA who has relevant training and adequate supervision. Over half this time is spent on clinical tasks. Conclusions The skills of AHAs are not being optimally utilised. Significant opportunity exists to reform the current allied health workforce. Such reform should result in increased capacity of the workforce to meet future demands. What is known about the topic? Increasing skill shortages across Australia’s health workforce necessitates that the capabilities of all healthcare team members should be used optimally. AHA roles are an important and growing response to current health workforce needs. Increasing workforce capacity will ensure the right health workers are matched to the right task by skill, experience and expertise. What does this paper add? This paper presents a model that assists services to identify tasks suitable for delegation to an AHA by an AHP. The model is unique because it describes a process that quantifies the need for AHAs and it has been successfully implemented in rural, regional and metropolitan health services in Victoria. What are the implications for practitioners? Working collaboratively, with executive support, will lead to a sustainable and integrated approach to support workforce capacity building. Altering the skill mix of healthcare teams through increasing the role of AHAs has benefits for AHPs, patients and the healthcare system.
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Qi, Xiaojuan, Wenjie Tang, Shan Gao, Min Gao, Changshui Chen i Qingye Zhang. "Design Synthesis and Biological Evaluation of NovelN-Nitro Acid Amide Derivatives as Lead Compounds of Herbicide". Journal of Chemistry 2016 (2016): 1–6. http://dx.doi.org/10.1155/2016/8583765.
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A series ofN-nitro acid amide derivatives compounds were synthesized based on the active site of target acetohydroxyacid synthase (AHAS, EC: 2.2.1.6) enzyme. All the structures of newly prepared compounds were thoroughly characterized by satisfied IR and1H NMR spectra. The IC50values against AHAS enzyme and EC50values for herbicidal activity againstAmaranthus mangostanus L.andSorghum sudanenseof all synthesized target compounds were determined. The compoundsII-10,II-21, andII-22with IC50values of 7.09 mg/L, 9.07 mg/L, and 9.11 mg/L and the compoundsII-8andII-22with EC50values of 9.87 mg/L and 19.88 mg/L against root ofAmaranthus mangostanus L.andSorghum sudanensewere illustrated, respectively. Meanwhile, the possible reasons for the lower activity of compounds were analyzed by molecular docking prediction.
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Gokhale, Kunal, i Bhargav Tilak. "Mechanisms of bacterial acetohydroxyacid synthase (ahas) and specific inhibitors of Mycobacterium tuberculosis ahas as potential drug candidates against tuberculosis". Current Drug Targets 16, nr 7 (27.07.2015): 689–99. http://dx.doi.org/10.2174/1389450116666150416115547.
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CHANG, Alan K., i Ronald G. DUGGLEBY. "Herbicide-resistant forms of Arabidopsis thaliana acetohydroxyacid synthase: characterization of the catalytic properties and sensitivity to inhibitors of four defined mutants". Biochemical Journal 333, nr 3 (1.08.1998): 765–77. http://dx.doi.org/10.1042/bj3330765.
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Acetohydroxyacid synthase (AHAS) catalyses the first step in the synthesis of the branched-chain amino acids and is the target of several classes of herbicides. Four mutants (A122V, W574S, W574L and S653N) of the AHAS gene from Arabidopsis thaliana were constructed, expressed in Escherichia coli, and the enzymes were purified. Each mutant form and wild-type was characterized with respect to its catalytic properties and sensitivity to nine herbicides. Each enzyme had a pH optimum near 7.5. The specific activity varied from 13% (A122V) to 131% (W574L) of the wild-type and the Km for pyruvate of the mutants was similar to the wild-type, except for W574L where it was five-fold higher. The activation by cofactors (FAD, Mg2+ and thiamine diphosphate) was examined. A122V showed reduced affinity for all three cofactors, whereas S653N bound FAD more strongly than wild-type AHAS. Six sulphonylurea herbicides inhibited A122V to a similar degree as the wild-type but S653N showed a somewhat greater reduction in sensitivity to these compounds. In contrast, the W574 mutants were insensitive to these sulphonylureas, with increases in the Kiapp (apparent inhibition constant) of several hundred fold. All four mutants were resistant to three imidazolinone herbicides with decreases in sensitivity ranging from 100-fold to more than 1000-fold.
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Krause, Felix S., Bastian Blombach i Bernhard J. Eikmanns. "Metabolic Engineering of Corynebacterium glutamicum for 2-Ketoisovalerate Production". Applied and Environmental Microbiology 76, nr 24 (15.10.2010): 8053–61. http://dx.doi.org/10.1128/aem.01710-10.
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ABSTRACT 2-Ketoisovalerate is used as a therapeutic agent, and a 2-ketoisovalerate-producing organism may serve as a platform for products deriving from this 2-keto acid. We engineered the wild type of Corynebacterium glutamicum for the growth-decoupled production of 2-ketoisovalerate from glucose by deletion of the aceE gene encoding the E1p subunit of the pyruvate dehydrogenase complex, deletion of the transaminase B gene ilvE, and additional overexpression of the ilvBNCD genes, encoding the l-valine biosynthetic enzymes acetohydroxyacid synthase (AHAS), acetohydroxyacid isomeroreductase, and dihydroxyacid dehydratase. 2-Ketoisovalerate production was further improved by deletion of the pyruvate:quinone oxidoreductase gene pqo. In fed-batch fermentations at high cell densities, the newly constructed strains produced up to 188 ± 28 mM (21.8 ± 3.2 g liter−1) 2-ketoisovalerate and showed a product yield of about 0.47 ± 0.05 mol per mol (0.3 ± 0.03 g per g) of glucose and a volumetric productivity of about 4.6 ± 0.6 mM (0.53 ± 0.07 g liter−1) 2-ketoisovalerate per h in the overall production phase. In studying the influence of the three branched-chain 2-keto acids 2-ketoisovalerate, 2-ketoisocaproate, and 2-keto-3-methylvalerate on the AHAS activity, we observed a competitive inhibition of the AHAS enzyme by 2-ketoisovalerate.
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Zajączkowska, Lidia, i Małgorzata Norek. "Peculiarities of Aluminum Anodization in AHAs-Based Electrolytes: Case Study of the Anodization in Glycolic Acid Solution". Materials 14, nr 18 (17.09.2021): 5362. http://dx.doi.org/10.3390/ma14185362.
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The anodization of aluminum (Al) in three alpha-hydroxy acids (AHAs): glycolic (GC), malic (MC), and citric (CC), was analyzed. Highly ordered pores in GC were obtained for the first time. However, the hexagonal cells were characterized by a non-uniform size distribution. Although common features of current density behavior are visible, the anodization in AHAs demonstrates some peculiarities. The electric conductivity (σ) of 0.5 M GC, MC, and CC electrolytes was in the following order: σ(CC) > σ(MC) > σ(GC), in accordance with the acid strength pKa(CC) < pKa(MC) < pKa(GC). However, the anodization voltage, under which a self-organized pore formation in anodic alumina (AAO) was observed (Umax), decreased with increasing pKa: Umax(CC) > Umax(MC) ≥ Umax(GC). This unusual behavior is most probably linked with the facility of acid ions to complex Al and the active participation of the Al complexes in the AAO formation. Depending on the AHA, its tendency and different modes to coordinate Al ions, the contribution of stable Al complexes to the AAO growth is different. It can be concluded that the structure of Al complexes, their molecular mass, and the ability to lose electrons play more important roles in the AAO formation than pKa values of AHAs.
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Ruppert, Claudia, Sönke Wimmers, Thorsten Lemker i Volker Müller. "The A1Ao ATPase fromMethanosarcina mazei: Cloning of the 5′ End of theaha Operon Encoding the Membrane Domain and Expression of the Proteolipid in a Membrane-Bound Form in Escherichia coli". Journal of Bacteriology 180, nr 13 (1.07.1998): 3448–52. http://dx.doi.org/10.1128/jb.180.13.3448-3452.1998.
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ABSTRACT Three additional ATPase genes, clustered in the orderahaH, ahaI, and ahaK, were found upstream of the previously characterized genes ahaECFABDGcoding for the archaeal A1Ao ATPase fromMethanosarcina mazei. ahaH, the first gene in the cluster, is preceded by a conserved promoter sequence. Northern blot analysis revealed that the clusters ahaHIK andahaECFABDG are transcribed as one message. AhaH is a hydrophilic polypeptide and is similar to peptides of previously unassigned function encoded by genes preceding postulated ATPase genes in Methanobacterium thermoautotrophicum andMethanococcus jannaschii. AhaI has a two-domain structure with a hydrophilic domain of 39 kDa and a hydrophobic domain with seven predicted transmembrane α helices. It is similar to the 100-kDa polypeptide of V1Vo ATPases and is therefore suggested to participate in proton transport. AhaK is a hydrophobic polypeptide with two predicted transmembrane α helices and, on the basis of sequence comparisons and immunological studies, is identified as the proteolipid, a polypeptide which is essential for proton translocation. However, it is only one-half and one-third the size of the proteolipids from M. thermoautotrophicum and M. jannaschii, respectively. ahaK is expressed inEscherichia coli, and it is incorporated into the cytoplasmic membrane despite the different chemical natures of lipids from archaea and bacteria. This is the first report on the expression and incorporation into E. coli lipids of a membrane integral enzyme from a methanogens, which will facilitate analysis of the structure and function of the membrane domain of the methanoarchaeal ATPase.
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Zwickel, Wolfgang. "Die kultreform des ahas (2 kön 16,10–18)". Scandinavian Journal of the Old Testament 7, nr 2 (styczeń 1993): 250–62. http://dx.doi.org/10.1080/09018329308585020.
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