Articoli di riviste: "Enzyme activation"

1

Wollenberger, Ulla, e Frieder W. Scheller. "Enzyme activation for activator and enzyme activity measurement☆". Biosensors and Bioelectronics 8, n. 6 (1993): 291–97. http://dx.doi.org/10.1016/0956-5663(93)85009-d.

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Wang, Fang, Yuchen Liu, Chang Du e Renjun Gao. "Current Strategies for Real-Time Enzyme Activation". Biomolecules 12, n. 5 (19 aprile 2022): 599. http://dx.doi.org/10.3390/biom12050599.

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Enzyme activation is a powerful means of achieving biotransformation function, aiming to intensify the reaction processes with a higher yield of product in a short time, and can be exploited for diverse applications. However, conventional activation strategies such as genetic engineering and chemical modification are generally irreversible for enzyme activity, and they also have many limitations, including complex processes and unpredictable results. Recently, near-infrared (NIR), alternating magnetic field (AMF), microwave and ultrasound irradiation, as real-time and precise activation strategies for enzyme analysis, can address many limitations due to their deep penetrability, sustainability, low invasiveness, and sustainability and have been applied in many fields, such as biomedical and industrial applications and chemical synthesis. These spatiotemporal and controllable activation strategies can transfer light, electromagnetic, or ultrasound energy to enzymes, leading to favorable conformational changes and improving the thermal stability, stereoselectivity, and kinetics of enzymes. Furthermore, the different mechanisms of activation strategies have determined the type of applicable enzymes and manipulated protocol designs that either immobilize enzymes on nanomaterials responsive to light or magnetic fields or directly influence enzymatic properties. To employ these effects to finely and efficiently activate enzyme activity, the physicochemical features of nanomaterials and parameters, including the frequency and intensity of activation methods, must be optimized. Therefore, this review offers a comprehensive overview related to emerging technologies for achieving real-time enzyme activation and summarizes their characteristics and advanced applications.

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Hamilton-Miller, J. M. T., e Q. Li. "Enzyme-Catalyzed Antimicrobial Activation". Antimicrobial Agents and Chemotherapy 46, n. 11 (1 novembre 2002): 3692. http://dx.doi.org/10.1128/aac.46.11.3692.2002.

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Hadfield, Andrea T. "Electron-Induced Enzyme Activation". Structure 14, n. 1 (gennaio 2006): 1–2. http://dx.doi.org/10.1016/j.str.2005.12.002.

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Bott, R., G. Ganshaw, M. Soltis, P. Kuhn e M. Knapp. "Snapshots of Enzyme Activation". Acta Crystallographica Section A Foundations of Crystallography 56, s1 (25 agosto 2000): s247. http://dx.doi.org/10.1107/s0108767300025319.

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6

Shisler, Krista A., Rachel U. Hutcheson, Masaki Horitani, Kaitlin S. Duschene, Adam V. Crain, Amanda S. Byer, Eric M. Shepard et al. "Monovalent Cation Activation of the Radical SAM Enzyme Pyruvate Formate-Lyase Activating Enzyme". Journal of the American Chemical Society 139, n. 34 (22 agosto 2017): 11803–13. http://dx.doi.org/10.1021/jacs.7b04883.

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7

Cassels, R., R. Fears e R. A. Smith. "The interaction of streptokinase.plasminogen activator complex, tissue-type plasminogen activator, urokinase and their acylated derivatives with fibrin and cyanogen bromide digest of fibrinogen. Relationship to fibrinolytic potency in vitro". Biochemical Journal 247, n. 2 (15 ottobre 1987): 395–400. http://dx.doi.org/10.1042/bj2470395.

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The effects of purified soluble fibrin and of fibrinogen fragments (fibrin mimic) on the activation of Lys-plasminogen (i.e. plasminogen residues 77-790) to plasmin by streptokinase.plasminogen activator complex and by tissue-type plasminogen activator were studied. Dissociation constants of both activators were estimated to lie in the range 90-160 nM (fibrin) and 16-60 nM (CNBr-cleavage fragments of fibrinogen). The kinetic mechanism for both types of activator comprised non-essential enzyme activation via a Rapid Equilibrium Ordered Bireactant sequence. In order to relate the fibrin affinity of plasminogen activators to their fibrinolytic potency, the rate of lysis of supported human plasma clots formed in the presence of unmodified or active-centre-acylated precursors of plasminogen activators was studied as a function of the concentration of enzyme derivative. The concentrations of unmodified enzyme giving 50% lysis/h in this assay were 0.9, 2.0 and 11.0 nM for tissue-type plasminogen activator, streptokinase.plasmin(ogen) and urokinase respectively. However, the potencies of active-centre-acylated derivatives of these enzymes suggested that acylated-tissue plasminogen activator and streptokinase.plasminogen complexes of comparable hydrolytic stability were of comparable potency. Both types of acyl-enzyme were significantly more potent than acyl-urokinases.

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Arcus, Vickery L., e Adrian J. Mulholland. "Temperature, Dynamics, and Enzyme-Catalyzed Reaction Rates". Annual Review of Biophysics 49, n. 1 (6 maggio 2020): 163–80. http://dx.doi.org/10.1146/annurev-biophys-121219-081520.

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We review the adaptations of enzyme activity to different temperatures. Psychrophilic (cold-adapted) enzymes show significantly different activation parameters (lower activation enthalpies and entropies) from their mesophilic counterparts. Furthermore, there is increasing evidence that the temperature dependence of many enzyme-catalyzed reactions is more complex than is widely believed. Many enzymes show curvature in plots of activity versus temperature that is not accounted for by denaturation or unfolding. This is explained by macromolecular rate theory: A negative activation heat capacity for the rate-limiting chemical step leads directly to predictions of temperature optima; both entropy and enthalpy are temperature dependent. Fluctuations in the transition state ensemble are reduced compared to the ground state. We show how investigations combining experiment with molecular simulation are revealing fundamental details of enzyme thermoadaptation that are relevant for understanding aspects of enzyme evolution. Simulations can calculate relevant thermodynamic properties (such as activation enthalpies, entropies, and heat capacities) and reveal the molecular mechanisms underlying experimentally observed behavior.

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Vater, C. A., H. Nagase e E. D. Harris. "Proactivator-dependent activation of procollagenase induced by treatment with EGTA". Biochemical Journal 237, n. 3 (1 agosto 1986): 853–58. http://dx.doi.org/10.1042/bj2370853.

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A new mechanism for activation of the proactivator of procollagenase [Vater, Nagase & Harris (1983) J. Biol. Chem. 258, 9374-9382] has been found. Collagenolytic and other proteolytic enzyme activities in the medium of cultured rabbit synovial fibroblasts were found to be activated by a new mechanism: short-term incubation at 37 degrees C performed in the presence of EGTA followed by replacement of Ca2+ during enzyme assay. The crucial event in procollagenase activation is the production of a functional activator enzyme. Activation of procollagenase in the culture medium did not occur when proactivator was removed by immunoprecipitation. Proteolytic activity of proactivator was fully activated, whereas procollagenase alone could not be activated by the same sequence. EGTA treatment of the culture medium at 0 degrees C did not result in enzyme activation if Ca2+ was replaced before incubation at 37 degrees C. Certain other bivalent metal ions (e.g. Sn2+, Cd2+, Zn2+ and Mn2+) could substitute for Ca2+ to stabilize the proactivator as a zymogen and therefore prevent the appearance of proteolytic activity in culture medium. Isolation of proactivator and procollagenase from EGTA-treated radiolabelled culture medium by immunoprecipitation and subsequent analyses by fluorography revealed that a time-dependent proteolysis of both molecules occurred after replacement of Ca2+ and incubation at 37 degrees C. However, comparison of enzyme activity with fluorographic analyses showed that the maximal activation of both enzymes was achieved before any detectable decrease in Mr. The results suggest that the activation of proactivator and the subsequent activation of procollagenase may be initiated by conformational changes in structure of the proactivator molecule produced by removal of stabilizing bivalent metal ions.

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KHOLODENKO, Boris N., e Guy C. BROWN. "Paradoxical control properties of enzymes within pathways: can activation cause an enzyme to have increased control?" Biochemical Journal 314, n. 3 (15 marzo 1996): 753–60. http://dx.doi.org/10.1042/bj3140753.

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It is widely assumed that within a metabolic pathway inhibition of an enzyme causes the control exerted by that enzyme over the flux through its own reaction to increase, whereas activation causes its control to decrease. This assumption forms the basis of a number of experimental methods. For a pathway conceptually divided into two enzyme groups connected via a single metabolite we have derived a general condition under which this assumption is false, and thus the pathway shows paradoxical control behaviour, i.e. increased control with activation and decreased control with inhibition of an enzyme or group of enzymes. Paradoxical control behaviour occurs widely when enzyme activity is altered by changing Km (if an enzyme is already close to saturation by its substrate), but may also occur with changes in Vmax. when the elasticity to the linking metabolite increases with its concentration (as in some cases of sigmoidal and exponential kinetics or for reactions catalysed by isoenzymes). These findings suggest that enzymes with sigmoidal kinetics may have low control in the absence of activation, but may gain control with activation, and thus have beneficial regulatory properties.

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Lee, Moo-Yeal, e Jonathan S. Dordick. "Enzyme activation for nonaqueous media". Current Opinion in Biotechnology 13, n. 4 (agosto 2002): 376–84. http://dx.doi.org/10.1016/s0958-1669(02)00337-3.

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Takegawa, Mai, Tsubasa Tagawa, Ayumi Ogata, Shigeru Shimamoto e Yuji Hidaka. "Enzyme Activation Mechanism of Cocoonase". Biophysical Journal 118, n. 3 (febbraio 2020): 532a. http://dx.doi.org/10.1016/j.bpj.2019.11.2919.

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13

Hung, Hui-Chih, Meng-Wei Kuo, Gu-Gang Chang e Guang-Yaw Liu. "Characterization of the functional role of allosteric site residue Asp102 in the regulatory mechanism of human mitochondrial NAD(P)+-dependent malate dehydrogenase (malic enzyme)". Biochemical Journal 392, n. 1 (8 novembre 2005): 39–45. http://dx.doi.org/10.1042/bj20050641.

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Human mitochondrial NAD(P)+-dependent malate dehydrogenase (decarboxylating) (malic enzyme) can be specifically and allosterically activated by fumarate. X-ray crystal structures have revealed conformational changes in the enzyme in the absence and in the presence of fumarate. Previous studies have indicated that fumarate is bound to the allosteric pocket via Arg67 and Arg91. Mutation of these residues almost abolishes the activating effect of fumarate. However, these amino acid residues are conserved in some enzymes that are not activated by fumarate, suggesting that there may be additional factors controlling the activation mechanism. In the present study, we tried to delineate the detailed molecular mechanism of activation of the enzyme by fumarate. Site-directed mutagenesis was used to replace Asp102, which is one of the charged amino acids in the fumarate binding pocket and is not conserved in other decarboxylating malate dehydrogenases. In order to explore the charge effect of this residue, Asp102 was replaced by alanine, glutamate or lysine. Our experimental data clearly indicate the importance of Asp102 for activation by fumarate. Mutation of Asp102 to Ala or Lys significantly attenuated the activating effect of fumarate on the enzyme. Kinetic parameters indicate that the effect of fumarate was mainly to decrease the Km values for malate, Mg2+ and NAD+, but it did not notably elevate kcat. The apparent substrate Km values were reduced by increasing concentrations of fumarate. Furthermore, the greatest effect of fumarate activation was apparent at low malate, Mg2+ or NAD+ concentrations. The Kact values were reduced with increasing concentrations of malate, Mg2+ and NAD+. The Asp102 mutants, however, are much less sensitive to regulation by fumarate. Mutation of Asp102 leads to the desensitization of the co-operative effect between fumarate and substrates of the enzyme.

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Park, Yong-Doo, Yi Yang, Qing-Xi Chen, Hai-Ning Lin, Qiang Liu e Hai-Meng Zhou. "Kinetics of complexing activation by the magnesium ion on green crab (Scylla serrata) alkaline phosphatase". Biochemistry and Cell Biology 79, n. 6 (1 dicembre 2001): 765–72. http://dx.doi.org/10.1139/o01-152.

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As with mammalian enzymes, green crab (Scylla serrata) alkaline phosphatase can be activated by Mg2+through a time-dependent course. The activation is mainly a Vmaxeffect. Tsou's method was used to study the kinetic course of activation. The results show that the enzyme was activated by a complexing scheme that had not been previously identified: the enzyme first reversibly and quickly binds Mg2+and then undergoes a slow reversible course to activation, with a relatively high activation energy (78 ± 4 kJ/mol) and a slow conformational change. The activation reaction is a single molecule reaction, and the apparent activation rate constant is independent of Mg2+concentration if the concentration is sufficiently high. The microscopic rate constants of activation and the association constant were determined from the measurements. The proposed scheme may also be applied to the Mg2+activation mechanism for mammalian enzyme, to explain why the activation rate is time-dependent and not diffusion controlled. Substrate binding was also shown to affect the activation rate constant.Key words: alkaline phosphatase, green crab, kinetics, activation, magnesium ion.

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BOATRIGHT, Kelly M., Cristina DEIS, Jean-Bernard DENAULT, Daniel P. SUTHERLIN e Guy S. SALVESEN. "Activation of caspases-8 and -10 by FLIPL". Biochemical Journal 382, n. 2 (24 agosto 2004): 651–57. http://dx.doi.org/10.1042/bj20040809.

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The first step in caspase activation is transition of the latent zymogen to an active form. For the initiator caspases, this occurs through dimerization of monomeric zymogens at an activating complex. Recent studies have suggested that FLIPL [FLICE-like inhibitory protein, long form; FLICE is FADD (Fas-associated death domain protein)-like interleukin-1β-converting enzyme], previously thought to act solely as an inhibitor of caspase-8 activation, can under certain circumstances function to enhance caspase activation. Using an in vitro induced-proximity assay, we demonstrate that activation of caspases-8 and -10 occurs independently of cleavage of either the caspase or FLIPL. FLIPL activates caspase-8 by forming heterodimeric enzyme molecules with substrate specificity and catalytic activity indistinguishable from those of caspase-8 homodimers. Significantly, the barrier for heterodimer formation is lower than that for homodimer formation, suggesting that FLIPL is a more potent activator of caspase-8 than is caspase-8 itself.

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Chau, Helen S., e Stephen K. Ng. "Activation of phosphoenolpyruvate carboxykinase isolated from Veillonella parvula". Biochemistry and Cell Biology 64, n. 9 (1 settembre 1986): 898–905. http://dx.doi.org/10.1139/o86-120.

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Phosphoenolpyruvate carboxykinase (PEPCK, EC 4.1.1.49) has been purified 940-fold from Veillonella parvula using protamine sulphate treatment, ammonium sulphate precipitation, and column chromatography. The purified enzyme was substantially free of contaminating enzymes or proteins. Maximum activity in the direction of oxaloacetate (OAA) decarboxylation was exhibited at pH 9.0. At this pH, the V. parvula enzyme catalysed phosphenolpyruvate formation in the presence of Mn2+ ions. In the presence of varying concentrations of OAA and ATP, the PEPCK from V. parvula exhibited hyperbolic kinetics with Kms of 0.16 and 0.46 mM, respectively. PEPCK from the anaerobe was not inhibited by NADH, succinate, glutamate, D-glucose 6-phosphate, acetyl phosphate, D-fructose 1,6-bisphosphate, pyruvate, ribose 5-phosphate, and aspartate. However, acetyl CoA, glyceraldehyde 3-phosphate, 3-phospho-D-glycerate, CTP, and GTP activated the enzyme. The activation of acetyl CoA was uncompetitive and noncooperative.

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Ghosh, S. K., S. Majumder, N. K. Mukhopadhyay e S. K. Bose. "Functional characterization of constituent enzyme fractions of mycobacillin synthetase". Biochemical Journal 230, n. 3 (15 settembre 1985): 785–89. http://dx.doi.org/10.1042/bj2300785.

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The enzyme fraction A, a constituent enzyme of the three-fraction enzyme mycobacillin synthetase, independently and sequentially activated five amino acids starting from L-proline, producing the pentapeptide Pro(Asp1,Glu1,Tyr1)Asp. The fractions B and C were unable to function independently. However, the fraction B synthesized the nonapeptide Pro(Asp3,Glu1,Tyr2,Ser1)Leu, sequentially activating the pentapeptide and next four amino acids, whereas the fraction C synthesized mycobacillin by the sequential activation of the nonapeptide and the remaining four amino acids. The pH optima of the above enzymes are almost identical (pH 7.8), but their Km values are a little different.

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Markovic, Milica, Shimon Ben-Shabat e Arik Dahan. "Computational Simulations to Guide Enzyme-Mediated Prodrug Activation". International Journal of Molecular Sciences 21, n. 10 (20 maggio 2020): 3621. http://dx.doi.org/10.3390/ijms21103621.

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Prodrugs are designed to improve pharmaceutical/biopharmaceutical characteristics, pharmacokinetic/pharmacodynamic properties, site-specificity, and more. A crucial step in successful prodrug is its activation, which releases the active parent drug, exerting a therapeutic effect. Prodrug activation can be based on oxidation/reduction processes, or through enzyme-mediated hydrolysis, from oxidoreductases (i.e., Cytochrome P450) to hydrolytic enzymes (i.e., carboxylesterase). This study provides an overview of the novel in silico methods for the optimization of enzyme-mediated prodrug activation. Computational methods simulating enzyme-substrate binding can be simpler like molecular docking, or more complex, such as quantum mechanics (QM), molecular mechanics (MM), and free energy perturbation (FEP) methods such as molecular dynamics (MD). Examples for MD simulations used for elucidating the mechanism of prodrug (losartan, paclitaxel derivatives) metabolism via CYP450 enzyme are presented, as well as an MD simulation for optimizing linker length in phospholipid-based prodrugs. Molecular docking investigating quinazolinone prodrugs as substrates for alkaline phosphatase is also presented, as well as QM and MD simulations used for optimal fit of different prodrugs within the human carboxylesterase 1 catalytical site. Overall, high quality computational simulations may show good agreement with experimental results, and should be used early in the prodrug development process.

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GRIGG, Michael E., Kleoniki GOUNARIS e Murray E. SELKIRK. "Characterization of a platelet-activating factor acetylhydrolase secreted by the nematode parasite Nippostrongylus brasiliensis". Biochemical Journal 317, n. 2 (15 luglio 1996): 541–47. http://dx.doi.org/10.1042/bj3170541.

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Nippostrongylus brasiliensis, a small nematode parasite of the gastrointestinal tract of rodents, secretes an enzyme that cleaves the proinflammatory molecule platelet-activating factor to its inactive lyso- form. The enzyme activity is Ca2+-dependent and does not exhibit interfacial activation. It does not require the addition of reducing agents for maximal activity, and is not inhibited by thiol-active reagents. Sensitivity to inhibitors suggests the involvement of serine and histidine residues in the enzyme activity. As described for other platelet-activating factor acetylhydrolases, it cannot cleave, nor is it inhibited by, long-chain diacyl phospholipids that are typical substrates for phospholipases A2. The purified enzyme was resolved by SDS/PAGE as a heterodimer composed of two protein subunits with apparent molecular masses of 38 and 25 kDa. The properties of the nematode enzyme thus differ from those described for the mammalian enzymes, but are more closely related to those of an acetylhydrolase than a phospholipase.

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Komatsu, Masayuki, Madhu Biyani, Sunita Ghimire Gautam e Koichi Nishigaki. "Peptide-Modulated Activity Enhancement of Acidic Protease Cathepsin E at Neutral pH". International Journal of Peptides 2012 (17 dicembre 2012): 1–7. http://dx.doi.org/10.1155/2012/316432.

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Enzymes are regulated by their activation and inhibition. Enzyme activators can often be effective tools for scientific and medical purposes, although they are more difficult to obtain than inhibitors. Here, using the paired peptide method, we report on protease-cathepsin-E-activating peptides that are obtained at neutral pH. These selected peptides also underwent molecular evolution, after which their cathepsin E activation capability improved. Thus, the activators we obtained could enhance cathepsin-E-induced cancer cell apoptosis, which indicated their potential as cancer drug precursors.

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Zhang, Wei-Wei, Kent Redman, Sharon Churchill e Perry Churchill. "Comparison of D-β-hydroxybutyrate dehydrogenase from rat liver and brain mitochondria". Biochemistry and Cell Biology 68, n. 10 (1 ottobre 1990): 1225–30. http://dx.doi.org/10.1139/o90-182.

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The properties of D-β-hydroxybutyrate dehydrogenase (BDH) from rat liver and brain mitochondria were compared to determine if isozymes of this enzyme exist in these tissues. The BDHs from these tissues behaved similarly during the purification process. The enzymes were indistinguishable by sodium dodecyl sulfate – polyacrylamide or acid-urea – polyacrylamide gel electrophoresis and they had identical isoelectric points. The BDHs from rat liver and brain were also quite similar in functional parameters determined by kinetic analysis and phospholipid activation of apo-BDH (i.e., the lipid-free enzyme). Antiserum against rat liver BDH inhibited both enzymes to an equivalent extent in a titration assay. The enzymes had similar patterns of peptide mapping by partial digestion with Staphylococcus aureus V8 protease, followed by immunoblotting using antiserum against the liver enzyme. These results suggest that the BDHs in rat liver and brain are very similar and possibly identical.Key words: D-β-hydroxybutyrate dehydrogenase, membrane-bound enzyme, lipid activation.

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Anderson, Louise, e Per Gardeström. "Reductive light activation of enzyme activity". Physiologia Plantarum 110, n. 3 (18 luglio 2008): 295. http://dx.doi.org/10.1111/j.1399-3054.2000.1100301.x.

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Rana, S., N. Pozzi, L. A. Pelc e E. Di Cera. "Redesigning allosteric activation in an enzyme". Proceedings of the National Academy of Sciences 108, n. 13 (22 febbraio 2011): 5221–25. http://dx.doi.org/10.1073/pnas.1018860108.

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Rooseboom, Martijn, Jan N. M. Commandeur e Nico P. E. Vermeulen. "Enzyme-Catalyzed Activation of Anticancer Prodrugs". Pharmacological Reviews 56, n. 1 (marzo 2004): 53–102. http://dx.doi.org/10.1124/pr.56.1.3.

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Anderson, Louise, e Per Gardestrom. "Reductive light activation of enzyme activity". Physiologia Plantarum 110, n. 3 (novembre 2000): 295. http://dx.doi.org/10.1034/j.1399-3054.2000.1100301.x.

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Yang, Yan-hui, Herve Aloysius, Daigo Inoyama, Yu Chen e Long-qin Hu. "Enzyme-mediated hydrolytic activation of prodrugs". Acta Pharmaceutica Sinica B 1, n. 3 (ottobre 2011): 143–59. http://dx.doi.org/10.1016/j.apsb.2011.08.001.

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Sharrock, Abigail V., Jeff S. Mumm, Elsie M. Williams, Narimantas Čėnas, Jeff B. Smaill, Adam V. Patterson, David F. Ackerley, Gintautas Bagdžiūnas e Vickery L. Arcus. "Structural Evaluation of a Nitroreductase Engineered for Improved Activation of the 5-Nitroimidazole PET Probe SN33623". International Journal of Molecular Sciences 25, n. 12 (15 giugno 2024): 6593. http://dx.doi.org/10.3390/ijms25126593.

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Bacterial nitroreductase enzymes capable of activating imaging probes and prodrugs are valuable tools for gene-directed enzyme prodrug therapies and targeted cell ablation models. We recently engineered a nitroreductase (E. coli NfsB F70A/F108Y) for the substantially enhanced reduction of the 5-nitroimidazole PET-capable probe, SN33623, which permits the theranostic imaging of vectors labeled with oxygen-insensitive bacterial nitroreductases. This mutant enzyme also shows improved activation of the DNA-alkylation prodrugs CB1954 and metronidazole. To elucidate the mechanism behind these enhancements, we resolved the crystal structure of the mutant enzyme to 1.98 Å and compared it to the wild-type enzyme. Structural analysis revealed an expanded substrate access channel and new hydrogen bonding interactions. Additionally, computational modeling of SN33623, CB1954, and metronidazole binding in the active sites of both the mutant and wild-type enzymes revealed key differences in substrate orientations and interactions, with improvements in activity being mirrored by reduced distances between the N5-H of isoalloxazine and the substrate nitro group oxygen in the mutant models. These findings deepen our understanding of nitroreductase substrate specificity and catalytic mechanisms and have potential implications for developing more effective theranostic imaging strategies in cancer treatment.

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LEE, Sang Hyoung, J. David JOHNSON, Michael P. WALSH, Jacquelyn E. VAN LIEROP, Cindy SUTHERLAND, Ande XU, Wayne A. SNEDDEN et al. "Differential regulation of Ca2+/calmodulin-dependent enzymes by plant calmodulin isoforms and free Ca2+ concentration". Biochemical Journal 350, n. 1 (9 agosto 2000): 299–306. http://dx.doi.org/10.1042/bj3500299.

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Multiple calmodulin (CaM) isoforms are expressed in plants, but their biochemical characteristics are not well resolved. Here we show the differential regulation exhibited by two soya bean CaM isoforms (SCaM-1 and SCaM-4) for the activation of five CaM-dependent enzymes, and the Ca2+ dependence of their target enzyme activation. SCaM-1 activated myosin light-chain kinase as effectively as brain CaM (Kact 1.8 and 1.7nM respectively), but SCaM-4 produced no activation of this enzyme. Both CaM isoforms supported near maximal activation of CaM-dependent protein kinase II (CaM KII), but SCaM-4 exhibited approx.12-fold higher Kact than SCaM-1 for CaM KII phosphorylation of caldesmon. The SCaM isoforms showed differential activation of plant and animal Ca2+-ATPases. The plant Ca2+-ATPase was activated maximally by both isoforms, while the erythrocyte Ca2+-ATPase was activated only by SCaM-1. Plant glutamate decarboxylase was activated fully by SCaM-1, but SCaM-4 exhibited an approx. 4-fold increase in Kact and an approx. 25% reduction in Vmax. Importantly, SCaM isoforms showed a distinct Ca2+ concentration requirement for target enzyme activation. SCaM-4 required 4-fold higher [Ca2+] for half-maximal activation of CaM KII, and 1.5-fold higher [Ca2+] for activation of cyclic nucleotide phosphodiesterase than SCaM-1. Thus these plant CaM isoforms provide a mechanism by which a different subset of target enzymes could be activated or inhibited by the differential expression of these CaM isoforms or by differences in Ca2+ transients.

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Cárdenas, M. L., e A. Cornish-Bowden. "Characteristics necessary for an interconvertible enzyme cascade to generate a highly sensitive response to an effector". Biochemical Journal 257, n. 2 (15 gennaio 1989): 339–45. http://dx.doi.org/10.1042/bj2570339.

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A monocyclic interconvertible enzyme cascade, in which active and inactive states of an enzyme are interconverted by two opposing enzyme-catalysed reactions, does not necessarily produce a greater degree of sensitivity to an effector than one could expect from direct interaction between effector and target reaction. On the contrary, a cascade in which an effector acts on one of the enzymes catalysing the interconversion reactions by altering the apparent value of its specificity constant will always generate a less sensitive response than direct interaction would give. Nonetheless, even if both interconversion reactions obey Michaelis-Menten kinetics with the ordinary types of inhibition and activation, one can easily generate an enormous sensitivity in which a 0.5% change in concentration can increase the proportion of target enzyme in the active state from 10% to 90%: this corresponds approximately to a Hill coefficient of 800. To maximize the sensitivity, the following conditions must be satisfied: (1) both modifier enzymes must act under conditions of near saturation; (2) the effector must act on both of them in opposite directions; (3) it must alter the apparent values of their catalytic constants; (4) the enzyme subject to inhibition by the effector must respond at much lower effector concentrations than the enzyme subject to activation. As the last of these conditions appears to be counter-intuitive, it suggests that feeble activation of modifier enzymes in real systems may have passed unnoticed, or been dismissed as physiologically insignificant, although in reality crucial to the effective response of the system.

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Pederick, Jordan L., Andrew P. Thompson, Stephen G. Bell e John B. Bruning. "d-Alanine–d-alanine ligase as a model for the activation of ATP-grasp enzymes by monovalent cations". Journal of Biological Chemistry 295, n. 23 (25 aprile 2020): 7894–904. http://dx.doi.org/10.1074/jbc.ra120.012936.

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The ATP-grasp superfamily of enzymes shares an atypical nucleotide-binding site known as the ATP-grasp fold. These enzymes are involved in many biological pathways in all domains of life. One ATP-grasp enzyme, d-alanine–d-alanine ligase (Ddl), catalyzes ATP-dependent formation of the d-alanyl–d-alanine dipeptide essential for bacterial cell wall biosynthesis and is therefore an important antibiotic drug target. Ddl is activated by the monovalent cation (MVC) K+, but despite its clinical relevance and decades of research, how this activation occurs has not been elucidated. We demonstrate here that activating MVCs bind adjacent to the active site of Ddl from Thermus thermophilus and used a combined biochemical and structural approach to characterize MVC activation. We found that TtDdl is a type II MVC-activated enzyme, retaining activity in the absence of MVCs. However, the efficiency of TtDdl increased ∼20-fold in the presence of activating MVCs, and it was maximally activated by K+ and Rb+ ions. A strict dependence on ionic radius of the MVC was observed, with Li+ and Na+ providing little to no TtDdl activation. To understand the mechanism of MVC activation, we solved crystal structures of TtDdl representing distinct catalytic stages in complex with K+, Rb+, or Cs+. Comparison of these structures with apo TtDdl revealed no evident conformational change on MVC binding. Of note, the identified MVC binding site is structurally conserved within the ATP-grasp superfamily. We propose that MVCs activate Ddl by altering the charge distribution of its active site. These findings provide insight into the catalytic mechanism of ATP-grasp enzymes.

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31

EDWARDS, Robert A., Michael P. WALSH, Cindy SUTHERLAND e Hans J. VOGEL. "Activation of calcineurin and smooth muscle myosin light chain kinase by Met-to-Leu mutants of calmodulin". Biochemical Journal 331, n. 1 (1 aprile 1998): 149–52. http://dx.doi.org/10.1042/bj3310149.

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The effects of replacement of each of the individual Met in calmodulin (CaM) with Leu on the activation of two CaM target enzymes [smooth muscle myosin light chain kinase (smMLCK) and calcineurin (CN)] were investigated. The KD and Pmax (percentage maximal activation) values for activation of both enzymes by M76L-CaM were indistinguishable from wild-type (wt)-CaM, which is consistent with the location of Met-76 in the central linker that is not involved in target protein interaction. The other eight Met in CaM are exposed in the hydrophobic surfaces that are involved in target-enzymes binding, and in general equivalent effects are observed for substitutions of Leu for Met residues in homologous positions in the two CaM domains. However, the importance of the interaction of specific Met residues with the target enzyme depends on the particular enzyme. Leu substitution at Met-36 or Met-109 reduced the affinity of MLCK for the mutant and the maximal activation of CN. MLCK had a higher KD for M51L-CaM whereas M124L-CaM activated the kinase to only 68% of maximal activity induced by wt-CaM; these mutants were indistinguishable from wt-CaM in activation of CN. M71L- and M144L-CaMs behaved like wt-CaM in activation of MLCK, but activated the phosphatase to only about 80% of maximal activity induced by wt-CAM. M72L-CaM exhibited an increased affinity for MLCK compared to wt-CaM and slightly decreased maximal activation, whereas M145L-CaM exhibited maximal activation significantly greater than that due to wt-CaM; these mutants behaved like wt-CaM with respect to CN activation. Finally, a mutant CaM in which all four C-terminal Met were replaced by Leu (M4-CT-L4-CaM) had similar affinities for MLCK and CN as wt-CaM but maximal activation of these enzymes by this mutant was only 60–70% of that achieved with wt-CaM. These results imply that, in addition to removing the autoinhibitory domain from the active site of the target enzyme, CaM must induce a conformational change in the active site itself.

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32

Plafker, Scott M., Kendra S. Plafker, Allan M. Weissman e Ian G. Macara. "Ubiquitin charging of human class III ubiquitin-conjugating enzymes triggers their nuclear import". Journal of Cell Biology 167, n. 4 (15 novembre 2004): 649–59. http://dx.doi.org/10.1083/jcb.200406001.

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Ubiquitin is a small polypeptide that is conjugated to proteins and commonly serves as a degradation signal. The attachment of ubiquitin (Ub) to a substrate proceeds through a multi-enzyme cascade involving an activating enzyme (E1), a conjugating enzyme (E2), and a protein ligase (E3). We previously demonstrated that a murine E2, UbcM2, is imported into nuclei by the transport receptor importin-11. We now show that the import mechanism for UbcM2 and two other human class III E2s (UbcH6 and UBE2E2) uniquely requires the covalent attachment of Ub to the active site cysteine of these enzymes. This coupling of E2 activation and transport arises from the selective interaction of importin-11 with the Ub-loaded forms of these enzymes. Together, these findings reveal that Ub charging can function as a nuclear import trigger, and identify a novel link between E2 regulation and karyopherin-mediated transport.

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33

Marshall, Andrew C., e John B. Bruning. "Engineering potassium activation into biosynthetic thiolase". Biochemical Journal 478, n. 15 (13 agosto 2021): 3047–62. http://dx.doi.org/10.1042/bcj20210455.

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Activation of enzymes by monovalent cations (M+) is a widespread phenomenon in biology. Despite this, there are few structure-based studies describing the underlying molecular details. Thiolases are a ubiquitous and highly conserved family of enzymes containing both K+-activated and K+-independent members. Guided by structures of naturally occurring K+-activated thiolases, we have used a structure-based approach to engineer K+-activation into a K+-independent thiolase. To our knowledge, this is the first demonstration of engineering K+-activation into an enzyme, showing the malleability of proteins to accommodate M+ ions as allosteric regulators. We show that a few protein structural features encode K+-activation in this class of enzyme. Specifically, two residues near the substrate-binding site are sufficient for K+-activation: A tyrosine residue is required to complete the K+ coordination sphere, and a glutamate residue provides a compensating charge for the bound K+ ion. Further to these, a distal residue is important for positioning a K+-coordinating water molecule that forms a direct hydrogen bond to the substrate. The stability of a cation–π interaction between a positively charged residue and the substrate is determined by the conformation of the loop surrounding the substrate-binding site. Our results suggest that this cation–π interaction effectively overrides K+-activation, and is, therefore, destabilised in K+-activated thiolases. Evolutionary conservation of these amino acids provides a promising signature sequence for predicting K+-activation in thiolases. Together, our structural, biochemical and bioinformatic work provide important mechanistic insights into how enzymes can be allosterically activated by M+ ions.

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34

Trusek, Anna. "Graphene oxide flake activation via divinylsulfone – a procedure for efficient β-galactosidase immobilization". Polish Journal of Chemical Technology 21, n. 1 (1 marzo 2019): 27–32. http://dx.doi.org/10.2478/pjct-2019-0006.

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Abstract Flaky graphene oxide was activated with divinylsulfone followed by immobilization of the β-galactosidase enzyme. An active and stable preparation was obtained. β-galactosidase stability after immobilization was much higher than with the native enzyme. The half-life time of the immobilized enzyme was estimated as 165 hours, while for the native form, the estimate was only 5 hours. The developed procedure for the preparation of flaked graphene and its use in the chemical immobilization of enzymes can be used for any enzyme. A processing solution for continuous operation was proposed and verified using cow’s milk, with lactose as the hydrolysed substrate, as a dosing stream. Lactose, a milk sugar, was effectively hydrolysed. Product for allergy sufferers who cannot digest lactose has been obtained in this way.

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35

Chosa, Naoyuki, Takashi Fukumitsu, Kengo Fujimoto e Eiji Ohnishi. "Activation of prophenoloxidase A1 by an activating enzyme in Drosophila melanogaster". Insect Biochemistry and Molecular Biology 27, n. 1 (gennaio 1997): 61–68. http://dx.doi.org/10.1016/s0965-1748(96)00070-7.

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36

Pyatakova, N. V., e I. S. Severina. "Soluble guanylate cyclase in the molecular mechanism underlying the therapeutic action of drugs". Biomeditsinskaya Khimiya 58, n. 1 (gennaio 2012): 32–42. http://dx.doi.org/10.18097/pbmc20125801032.

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The influence of ambroxol - a mucolytic drug - on the activity of human platelet soluble guanylate cyclase and rat lung soluble guanylate cyclase and activation of both enzymes by NO-donors (sodium nitroprusside and Sin-1) were investigated. Ambroxol in the concentration range from 0.1 to 10 μM had no effect on the basal activity of both enzymes. Ambroxol inhibited in a concentration-dependent manner the sodium nitroprusside-induced human platelet soluble guanylate cyclase and rat lung soluble guanylate cyclase with the IC50 values 3.9 and 2.1 μM, respectively. Ambroxol did not influence the stimulation of both enzymes by protoporphyrin IX.The influence of artemisinin - an antimalarial drug - on human platelet soluble guanylate cyclase activity and the enzyme activation by NO-donors were investigated. Artemisinin (0.1-100 μM) had no effect on the basal activity of the enzyme. Artemisinin inhibited in a concentration-dependent manner the sodium nitroprusside-induced activation of human platelet guanylate cyclase with an IC50 value 5.6 μM. Artemisinin (10 μM) also inhibited (by 71±4.0%) the activation of the enzyme by thiol-dependent NO-donor the derivative of furoxan, 3,4-dicyano-1,2,5-oxadiazolo-2-oxide (10 μM), but did not influence the stimulation of soluble guanylate cyclase by protoporphyrin IX. It was concluded that the sygnalling system NO-soluble guanylate cyclase-cGMP is involved in the molecular mechanism of the therapeutic action of ambroxol and artemisinin.

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37

Saito, T., L. Small e UW Goodenough. "Activation of adenylyl cyclase in Chlamydomonas reinhardtii by adhesion and by heat". Journal of Cell Biology 122, n. 1 (1 luglio 1993): 137–47. http://dx.doi.org/10.1083/jcb.122.1.137.

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Adhesion between Chlamydomonas reinhardtii gametes generates a rapid rise in cAMP levels which stimulates mating responses and zygotic cell fusion (Pasquale and Goodenough, 1987). We show here that sexual adhesion in vivo results in a twofold stimulation of flagellar adenylyl cyclase activity when the enzyme is subsequently assayed in vitro, a stimulation that is specifically blocked by Cd2+. A twofold stimulation is also elicited by the in vitro presentation of soluble cross-linking reagents (antisera and concanavalin A). In contrast, the 10-30-fold stimulation of the flagellar cyclase by in vitro exposure to 40 degrees C, first described by Zhang et al. (1991), is insensitive to Cd2+ but sensitive to such drugs as trifluoperizine and dibucaine. The capacity for twofold stimulation is displayed by the vegetative and gametic enzymes but is lost when gametes fuse to form zygotes; in contrast, the 10-fold stimulation is displayed by the gametic and zygotic enzymes but not the vegetative enzyme. The signal-defective mutant imp-3 fails to generate the normal mating-triggered cAMP production and can be rescued by exogenous dibutyryl cAMP. It displays normal basal rates of flagellar cyclase activity and a normal twofold stimulation by sexual adhesion and by soluble cross-linkers, but it is defective in 40 degrees C activation. The gametic cell-body adenylyl cyclase is stimulated when wild-type flagella, but not imp-3 flagella, undergo adhesive interactions in vivo, and it can be directly stimulated in vitro by cAMP presentation. We propose that the two levels of flagellar cyclase stimulation reflect either sequential steps in the activation of a single cyclase enzyme, with imp-3 blocked in the second step, or else the sequential activation of two different flagellar enzymes, with imp-3 defective in the second enzyme. We further propose that the cell-body enzyme is activated by the cAMP that is generated when flagellar cyclase activity is fully stimulated.

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38

Berger, Stefanie, Cornelia Welte e Uwe Deppenmeier. "Acetate Activation inMethanosaeta thermophila: Characterization of the Key Enzymes Pyrophosphatase and Acetyl-CoA Synthetase". Archaea 2012 (2012): 1–10. http://dx.doi.org/10.1155/2012/315153.

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The thermophilic methanogenMethanosaeta thermophilauses acetate as sole substrate for methanogenesis. It was proposed that the acetate activation reaction that is needed to feed acetate into the methanogenic pathway requires the hydrolysis of two ATP, whereas the acetate activation reaction inMethanosarcina sp.is known to require only one ATP. As these organisms live at the thermodynamic limit that sustains life, the acetate activation reaction inMt. thermophilaseems too costly and was thus reevaluated. It was found that of the putative acetate activation enzymes one gene encoding an AMP-forming acetyl-CoA synthetase was highly expressed. The corresponding enzyme was purified and characterized in detail. It catalyzed the ATP-dependent formation of acetyl-CoA, AMP, and pyrophosphate(PPi)and was only moderately inhibited byPPi. The breakdown ofPPiwas performed by a soluble pyrophosphatase. This enzyme was also purified and characterized. The pyrophosphatase hydrolyzed the major part ofPPi(KM=0.27±0.05 mM) that was produced in the acetate activation reaction. Activity was not inhibited by nucleotides orPPi. However, it cannot be excluded that otherPPi-dependent enzymes take advantage of the remainingPPiand contribute to the energy balance of the cell.

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39

Page, Michael J., e Enrico Di Cera. "Role of Na+and K+in Enzyme Function". Physiological Reviews 86, n. 4 (ottobre 2006): 1049–92. http://dx.doi.org/10.1152/physrev.00008.2006.

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Metal complexation is a key mediator or modifier of enzyme structure and function. In addition to divalent and polyvalent metals, group IA metals Na+and K+play important and specific roles that assist function of biological macromolecules. We examine the diversity of monovalent cation (M+)-activated enzymes by first comparing coordination in small molecules followed by a discussion of theoretical and practical aspects. Select examples of enzymes that utilize M+as a cofactor (type I) or allosteric effector (type II) illustrate the structural basis of activation by Na+and K+, along with unexpected connections with ion transporters. Kinetic expressions are derived for the analysis of type I and type II activation. In conclusion, we address evolutionary implications of Na+binding in the trypsin-like proteases of vertebrate blood coagulation. From this analysis, M+complexation has the potential to be an efficient regulator of enzyme catalysis and stability and offers novel strategies for protein engineering to improve enzyme function.

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40

Tiganescu, Ana, Melanie Hupe, Yoshikazu Uchida, Theodora Mauro, Peter M. Elias e Walter M. Holleran. "Increased glucocorticoid activation during mouse skin wound healing". Journal of Endocrinology 221, n. 1 (24 gennaio 2014): 51–61. http://dx.doi.org/10.1530/joe-13-0420.

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Glucocorticoid (GC) excess inhibits wound healing causing increased patient discomfort and infection risk. 11β-hydroxysteroid dehydrogenase type 1 (11β-HSD1) activates GCs (converting 11-dehydrocorticosterone to corticosterone in rodents) in many tissues including skin, wherede novosteroidogenesis from cholesterol has also been reported. To examine the regulation of 11β-HSD1 and steroidogenic enzyme expression during wound healing, 5 mm wounds were generated in female SKH1 mice and compared at days 0, 2, 4, 8, 14, and 21 relative to unwounded skin. 11β-HSD1 expression (mRNA and protein) and enzyme activity were elevated at 2 and 4 days post-wounding, with 11β-HSD1 localizing to infiltrating inflammatory cells. 11β-HSD2 (GC-deactivating) mRNA expression and activity were undetectable. Although several steroidogenic enzymes displayed variable expression during healing, expression of the final enzyme required for the conversion of 11-deoxycorticosterone to corticosterone, 11β-hydroxylase (CYP11B1), was lacking in unwounded skin and post-wounding. Consequently, 11-deoxycorticosterone was the principal progesterone metabolite in mouse skin before and after wounding. Our findings demonstrate that 11β-HSD1 activates considerably more corticosterone than is generatedde novofrom progesterone in mouse skin and drives GC exposure during healing, demonstrating the basis for 11β-HSD1 inhibitors to accelerate wound repair.

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41

Fillat, M. F., D. E. Edmondson e C. Gomez-Moreno. "Light-dependent de-activation/re-activation of Anabaena variabilis ferredoxin: NADP+ reductase". Biochemical Journal 274, n. 3 (15 marzo 1991): 781–86. http://dx.doi.org/10.1042/bj2740781.

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The activity of ferredoxin: NADP+ reductase (FNR) was found to decline to approximately 20% maximal levels with little or no loss in enzyme levels when cultures of the cyanobacterium Anabaena variabilis were maintained in the stationary phase of growth. Re-activation of enzyme activity occurred when cells were diluted into either fresh or re-utilized media and illuminated. This reversible de-activation/re-activation process was found, in vivo, to be dependent on the intensity of light illuminating the cells. The de-activated form of FNR was purified to homogeneity and exhibited the same molecular mass, isoelectric-focusing pattern and N-terminal amino acid sequence as the native form. Both de-activated and native FNR preparations each exhibited three reactive thiol groups on denaturation in urea; however, the rate of reaction with Ellman's reagent was much faster with the de-activated form than with the native form. Both preparations contain a single disulphide bond. Upon reduction of the disulphide bond in either form of the enzyme, the five reactive thiol groups exhibited identical reactivities in the presence of urea. Steady-state kinetic analysis of the de-activated form showed a marked increase in Km values for NADPH in diaphorase assays and an increase in Km for ferredoxin in the ferredoxin-mediated reduction of cytochrome c. No significant difference in kcat. was observed in comparison of the de-activated with the native form in any of the above assays; however, the de-activated form did exhibit a lower kcat. value in the transhydrogenase assay. The de-activated form of FNR bound ferredoxin with a 16-fold lower affinity than the native enzyme. These data suggest that the de-activation of FNR in vivo in response to low light intensity involves an alteration in protein structure, possibly via an intramolecular thiol disulphide interchange, which influences the interaction of the enzyme with its substrates.

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42

Tran, Giang Thi Linh, e Oanh Ngoc Huynh. "Preparation and immobilization Glucoamylase and Pectinase by CLEA method". Science and Technology Development Journal 17, n. 2 (30 giugno 2014): 45–51. http://dx.doi.org/10.32508/stdj.v17i2.1358.

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CLEA method (cross-linking enzyme aggregates) combines enzyme preparation and immobilization from solution culture into the same step. In this study, we applied CLEA method to immobilize two enzymes, glucoamylase and pectinase, from crude enzyme solution obtained from semi-solid culture of Aspergillus niger. The results showed that: In the same immobilized conditions (glucoamylase: 7% glutaraldehyde, 5°C, 2 hours; pectinase: 10% glutaraldehyde, 5°C, 2 hours), the immobilized enzyme from crude enzyme solution, has the abilities to be reused and activation stability under the influences of pH and temperature higher than immobilized commercial enzyme respectively.

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43

Kazemi, Masoud, Fahmi Himo e Johan Åqvist. "Enzyme catalysis by entropy without Circe effect". Proceedings of the National Academy of Sciences 113, n. 9 (11 gennaio 2016): 2406–11. http://dx.doi.org/10.1073/pnas.1521020113.

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Entropic effects have often been invoked to explain the extraordinary catalytic power of enzymes. In particular, the hypothesis that enzymes can use part of the substrate-binding free energy to reduce the entropic penalty associated with the subsequent chemical transformation has been very influential. The enzymatic reaction of cytidine deaminase appears to be a distinct example. Here, substrate binding is associated with a significant entropy loss that closely matches the activation entropy penalty for the uncatalyzed reaction in water, whereas the activation entropy for the rate-limiting catalytic step in the enzyme is close to zero. Herein, we report extensive computer simulations of the cytidine deaminase reaction and its temperature dependence. The energetics of the catalytic reaction is first evaluated by density functional theory calculations. These results are then used to parametrize an empirical valence bond description of the reaction, which allows efficient sampling by molecular dynamics simulations and computation of Arrhenius plots. The thermodynamic activation parameters calculated by this approach are in excellent agreement with experimental data and indeed show an activation entropy close to zero for the rate-limiting transition state. However, the origin of this effect is a change of reaction mechanism compared the uncatalyzed reaction. The enzyme operates by hydroxide ion attack, which is intrinsically associated with a favorable activation entropy. Hence, this has little to do with utilization of binding free energy to pay the entropic penalty but rather reflects how a preorganized active site can stabilize a reaction path that is not operational in solution.

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44

Demirkan, Elif, Tuba Avci e Yakup Aykut. "Protease immobilization on cellulose monoacetate/chitosan-blended nanofibers". Journal of Industrial Textiles 47, n. 8 (11 luglio 2017): 2092–111. http://dx.doi.org/10.1177/1528083717720205.

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Chitosan-blended cellulose monoacetate nanofibers were prepared through electrospinning process. Neat nanofibers and their sodium hydroxide-treated analogs were used as support surfaces for protease immobilization via physical adsorption method. Morphologies of the nanofibers were observed with a scanning electron microscopy. Chemical analyses were conducted with Fourier transform infrared spectroscopy, and thermal analyses were carried out with differential scanning calorimeter and thermogravimetric analyzer. Immobilized enzyme activities were measured by using casein substrate. In order to test the stability of immobilized enzymes, the tests were repeated until the immobilized enzyme activity was leveled off. The results reveal that well uniform cellulose monoacetate/chitosan nanofibers were obtained, and nanofiber structures are transformed from rounded to more flattened morphology after enzyme activation test. Glutaraldehyde activation has positive effect on sodium hydroxide-treated samples, and the highest immobilization yield as about 83% was observed for glutaraldehyde-treated cellulose monoacetate/chitosan samples. Sodium hydroxide treatment before glutaraldehyde activation shows the best results for protease immobilization on cellulose monoacetate and cellulose monoacetate/chitosan nanofibers. Operational stability increases after sodium hydroxide treatment and glutaraldehyde activation. Glutaraldehyde activation effectively increased the cycle number after sodium hydroxide treatment and about 20% of enzyme activity was still retained after seven cycles at cellulose monoacetate/chitosan samples. This percentage is higher at pure cellulose monoacetate nanofibers than cellulose monoacetate/chitosan nanofibers and measured around 33.5%.

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Edmund, Aaron B., Timothy F. Walseth, Nicholas M. Levinson e Lincoln R. Potter. "The pseudokinase domains of guanylyl cyclase–A and –B allosterically increase the affinity of their catalytic domains for substrate". Science Signaling 12, n. 566 (29 gennaio 2019): eaau5378. http://dx.doi.org/10.1126/scisignal.aau5378.

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Natriuretic peptides regulate multiple physiologic systems by activating transmembrane receptors containing intracellular guanylyl cyclase domains, such as GC-A and GC-B, also known as Npr1 and Npr2, respectively. Both enzymes contain an intracellular, phosphorylated pseudokinase domain (PKD) critical for activation of the C-terminal cGMP-synthesizing guanylyl cyclase domain. Because ATP allosterically activates GC-A and GC-B, we investigated how ATP binding to the PKD influenced guanylyl cyclase activity. Molecular modeling indicated that all the residues of the ATP-binding site of the prototypical kinase PKA, except the catalytic aspartate, are conserved in the PKDs of GC-A and GC-B. Kinase-inactivating alanine substitutions for the invariant lysine in subdomain II or the aspartate in the DYG-loop of GC-A and GC-B failed to decrease enzyme phosphate content, consistent with the PKDs lacking kinase activity. In contrast, both mutations reduced enzyme activation by blocking the ability of ATP to decrease the Michaelis constant without affecting peptide-dependent activation. The analogous lysine-to-alanine substitution in a glutamate-substituted phosphomimetic mutant form of GC-B also reduced enzyme activity, consistent with ATP stimulating guanylyl cyclase activity through an allosteric, phosphorylation-independent mechanism. Mutations designed to rigidify the conserved regulatory or catalytic spines within the PKDs increased guanylyl cyclase activity, increased sensitivity to natriuretic peptide, or reduced the Michaelis constant in the absence of ATP, consistent with ATP binding stabilizing the PKD in a conformation analogous to that of catalytically active kinases. We conclude that allosteric mechanisms evolutionarily conserved in the PKDs promote the catalytic activation of transmembrane guanylyl cyclases.

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46

Iwase, Katsumi, Brian C. W. Hummel e Paul G. Walfish. "Cytosol components from human placenta and rat liver in iodothyronine 5- and 5′-deiodination". Biochemistry and Cell Biology 67, n. 1 (1 gennaio 1989): 58–63. http://dx.doi.org/10.1139/o89-009.

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Using either human placental microsomal 5-deiodinase as enzyme (5-DI) and thyroxine as substrate or rat liver (RL) microsomal 5′-deiodinase (5′ DI) as enzyme and reverse [(3′- or 5′-)-125I]triiodo-L-thyronine ([125I]rT3) as substrate, activation of 5′-DI in the presence of NADPH was observed using either human placental or rat liver cytosolic components, but there was no activation of 5-DI. Both could be activated by DTT, with higher concentrations being required for 5-DI than for 5′-DI. Iopanoic acid, dicumarol, and sodium arsenite inhibited 5′-DI and 5-DI activated by DTT. In the presence of DTT, 1 mM 6-propyl-2-thiouracil had no effect on 5-DI but inhibited 5′ DI. Thus, human placental and rat liver cytosolic components are interchangeable in activating hepatic 5′-DI in the presence of NADPH. However, if an endogenous cofactor system involved in the activation of human placental 5-DI exists, it probably differs from the activator of liver 5′-DI.Key words: iodothyronines, deiodination cofactors, placenta, liver, cytosol.

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47

Huppe, Heather C., e Bob B. Buchanan. "Activation of a Chloroplast Type of Fructose Bisphosphatase from Chlamydomonas reinhardtii by Light-Mediated Agents". Zeitschrift für Naturforschung C 44, n. 5-6 (1 giugno 1989): 487–94. http://dx.doi.org/10.1515/znc-1989-5-624.

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Abstract A chloroplast type of fructose-1,6 -bisphosphatase, a central regulatory enzyme of photosynthetic carbon metabolism, has been partially purified from Chlamydomonas reinhardtii. Unlike its counterpart from spinach chloroplasts, the algal FBPase showed a strict requirement for a dithiol reductant irrespective of Mg2+ concentration. The enzymes from the two sources resembled each other immunologically, in subunit molecular mass and response to pH. In the presence of dithiothreitol, the pH optimum for both the algal and spinach enzymes shifted from 8.5 to a more physiological value of 8.0 as the Mg2+ concentration was increased from 1 to 16 mᴍ . At 1 mᴍ Mg2+, a concentration estimated to be close to physiological, the Chlamydomonas FBPase was active only in the presence of reduced thioredoxin and was most active with Chlamydomonas thioredoxin f. Under these conditions, the enzyme showed a pH optimum of 8.0. The data suggest that the Chlamydomonas enzyme resembles its spinach counterpart in most respects, but it has a stricter requirement for reduction and less strict reductant specificity. A comparison of the properties of the FBPases from Chlamydomonas and spinach will be helpful for elucidating the mechanism of the reductive activation of this enzyme.

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48

Hua, Jia-Dong, Lu Liu e Yi-Ming Qiu. "Activation of Polymer-Metal Complexes on Enzyme". Journal of Macromolecular Science: Part A - Chemistry 26, n. 2-3 (febbraio 1989): 495–504. http://dx.doi.org/10.1080/00222338908051989.

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49

Molski, Andrzej. "A Model of Diffusion-Influenced Enzyme Activation". Journal of Physical Chemistry B 104, n. 18 (maggio 2000): 4532–36. http://dx.doi.org/10.1021/jp9935844.

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50

Serdakowski, Anne L., e Jonathan S. Dordick. "Enzyme activation for organic solvents made easy". Trends in Biotechnology 26, n. 1 (gennaio 2008): 48–54. http://dx.doi.org/10.1016/j.tibtech.2007.10.007.

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