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Rodrigues, Marta V., Nuno Borges, Mafalda Henriques, Pedro Lamosa, Rita Ventura, Chantal Fernandes, Nuno Empadinhas, Christopher Maycock, Milton S. da Costa i Helena Santos. "Bifunctional CTP:Inositol-1-Phosphate Cytidylyltransferase/CDP-Inositol:Inositol-1-Phosphate Transferase, the Key Enzyme for Di-myo-Inositol-Phosphate Synthesis in Several (Hyper)thermophiles". Journal of Bacteriology 189, nr 15 (25.05.2007): 5405–12. http://dx.doi.org/10.1128/jb.00465-07.
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ABSTRACT The pathway for the synthesis of di-myo-inositol-phosphate (DIP) was recently elucidated on the basis of the detection of the relevant activities in cell extracts of Archaeoglobus fulgidus and structural characterization of products by nuclear magnetic resonance (NMR) (N. Borges, L. G. Gonçalves, M. V. Rodrigues, F. Siopa, R. Ventura, C. Maycock, P. Lamosa, and H. Santos, J. Bacteriol. 188:8128-8135, 2006). Here, a genomic approach was used to identify the genes involved in the synthesis of DIP. Cloning and expression in Escherichia coli of the putative genes for CTP:l-myo-inositol-1-phosphate cytidylyltransferase and DIPP (di-myo-inositol-1,3′-phosphate-1′-phosphate, a phosphorylated form of DIP) synthase from several (hyper)thermophiles (A. fulgidus, Pyrococcus furiosus, Thermococcus kodakaraensis, Aquifex aeolicus, and Rubrobacter xylanophilus) confirmed the presence of those activities in the gene products. The DIPP synthase activity was part of a bifunctional enzyme that catalyzed the condensation of CTP and l-myo-inositol-1-phosphate into CDP-l-myo-inositol, as well as the synthesis of DIPP from CDP-l-myo-inositol and l-myo-inositol-1-phosphate. The cytidylyltransferase was absolutely specific for CTP and l-myo-inositol-1-P; the DIPP synthase domain used only l-myo-inositol-1-phosphate as an alcohol acceptor, but CDP-glycerol, as well as CDP-l-myo-inositol and CDP-d-myo-inositol, were recognized as alcohol donors. Genome analysis showed homologous genes in all organisms known to accumulate DIP and for which genome sequences were available. In most cases, the two activities (l-myo-inositol-1-P cytidylyltransferase and DIPP synthase) were fused in a single gene product, but separate genes were predicted in Aeropyrum pernix, Thermotoga maritima, and Hyperthermus butylicus. Additionally, using l-myo-inositol-1-phosphate labeled on C-1 with carbon 13, the stereochemical configuration of all the metabolites involved in DIP synthesis was established by NMR analysis. The two inositol moieties in DIP had different stereochemical configurations, in contradiction of previous reports. The use of the designation di-myo-inositol-1,3′-phosphate is recommended to facilitate tracing individual carbon atoms through metabolic pathways.
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Stephens, L. R., R. R. Kay i R. F. Irvine. "A myo-inositol d-3 hydroxykinase activity in Dictyostelium". Biochemical Journal 272, nr 1 (15.11.1990): 201–10. http://dx.doi.org/10.1042/bj2720201.
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A soluble ATP-dependent enzyme which phosphorylates myo-inositol has been characterized in Dictyostelium. The myo-inositol kinase activity was partially purified from amoebae by chromatography on DEAE-Sepharose and phenyl-Sepharose columns. The product of both the partially purified activity and of a crude cytosolic fraction was myo-inositol 3-phosphate. The partially purified preparations of myo-inositol kinase (a) possessed a Km for myo-inositol of 120 microM (in the presence of 5 mM-ATP) and for ATP of 125 microM (in the presence of 1 microM-myo-inositol), (b) did not recognize allo-, epi-, muco-, neo-, scyllo-, 1 D-chiro or 1 L-chiro-inositol as substrates, (c) were competitively inhibited by three naturally occurring analogues of myo-inositol: 1 L-chiro-inositol (Ki 49.5 +/- 0.7 microM: the structural equivalent of myo-inositol, except that the D-3 hydroxy moiety is axial), D-3-deoxy-myo-inositol [Ki 103 +/- 1 microM: (-)-viburnitol], and sequoyitol (Ki 271 +/- 7 microM; unlike 1 L-chiro-inositol and D-3-deoxy-myo-inositol, this was a substrate for the kinase), and finally (d) were apparently non-competitively inhibited by myo-inositol 3-phosphate. The product of myo-inositol kinase could be detected in intact amoebae and was a substrate for the first in a series of inositol polyphosphate kinases present in Dictyostelium which ultimately yield myo-inositol hexakisphosphate. The activity of myo-inositol D-3-hydroxykinase in Dictyostelium lysates showed evidence of developmental regulation.
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Burtle, G. J., i R. T. Lovell. "Lack of Response of Channel Catfish (Ictalurus punctatus) to Dietary Myo-inositol". Canadian Journal of Fisheries and Aquatic Sciences 46, nr 2 (1.02.1989): 218–22. http://dx.doi.org/10.1139/f89-030.
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Channel catfish (Ictalurus punctatus) fingerlings were fed for 28 wk in aquaria (28 ± 1 °C) on semipurified diets with supplemental myo-inositol (400 mg∙kg diet−1), without myo-inositol, and without myo-inositol but with succinylsulfathiazole to suppress intestinal bacteria synthesis. Omission of myo-inositol from the diet, with or without the antibiotic, did not reduce growth rate, produce overt signs of myo-inositol deficiency, or cause a decrease in tissue (muscle, liver, and brain) concentration of myo-inositol. No lipid accumulation occurred in liver or kidney when myoinositol was deleted from the diet. The only possible lipotropic effect of myo-inositol deficiency was a slightly higher (P < 0.07) amount of lipid in brain tissue. Myo-inositol synthesis by enzymes in liver and brain tissues was not affected by myo-inositol in the diet. Rates of myo-inositol synthesis were 39.8 and 67.3 μmol∙h−1∙g protein−1 for liver and brain, which are higher than synthesis rates reported in rodents (myo-inositol synthesis has not been measured in other fish). This study showed that de novo synthesis of myo-inositol by fingerling channel catfish was sufficient for normal growth and maintenance of tissue levels of myo-inositol and to prevent overt signs of myo-inositol deficiency when the vitamin was not included in the diet.
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Stephens, L. R., P. T. Hawkins, A. F. Stanley, T. Moore, D. R. Poyner, P. J. Morris, M. R. Hanley, R. R. Kay i R. F. Irvine. "myo-inositol pentakisphosphates. Structure, biological occurrence and phosphorylation to myo-inositol hexakisphosphate". Biochemical Journal 275, nr 2 (15.04.1991): 485–99. http://dx.doi.org/10.1042/bj2750485.
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1. Standard and high-performance anion-exchange-chromatographic techniques have been used to purify myo-[3H]inositol pentakisphosphates from various myo-[3H]inositol-prelabelled cells. Slime mould (Dictyostelium discoideum) contained 8 microM-myo-[3H]inositol 1,3,4,5,6-pentakisphosphate, 16 microM-myo-[3H]inositol 1,2,3,4,6-pentakisphosphate and 36 microM-D-myo-[3H]inositol 1,2,4,5,6-pentakisphosphate [calculated intracellular concentrations; Stephens & Irvine (1990) Nature (London) 346, 580-583]; germinating mung-bean (Phaseolus aureus) seedlings contained both D- and L-myo-[3H]inositol 1,2,4,5,6-pentakisphosphate (which was characterized by 31P and two-dimensional proton n.m.r.) and D- and/or L-myo-[3H]inositol 1,2,3,4,5-pentakisphosphate; HL60 cells contained myo-[3H]inositol 1,3,4,5,6-pentakisphosphate (in a 500-fold excess over the other species), myo-[3H]inositol 1,2,3,4,6-pentakisphosphate and D- and/or L-myo-[3H]inositol 1,2,4,5,6-pentakisphosphate; and NG-115-401L-C3 cells contained myo-[3H]inositol 1,3,4,5,6-pentakisphosphate (in a 100-fold excess over the other species), D- and/or L-myo-[3H]inositol 1,2,4,5,6-pentakisphosphate, myo-[3H]inositol 1,2,3,4,6-pentakisphosphate and D- and/or L-myo-[3H]inositol 1,2,3,4,5-pentakisphosphate. 2. Multiple soluble ATP-dependent myo-inositol pentakisphosphate kinase activities have been detected in slime mould, rat brain and germinating mung-bean seedling homogenates. In slime-mould cytosolic fractions, the three myo-inositol pentakisphosphates that were present in intact slime moulds could be phosphorylated to myo-[3H]inositol hexakisphosphate: the relative first-order rate constants for these reactions were, in the order listed above, 1:8:31 respectively (with first-order rate constants in the intact cell of 0.1, 0.8 and 3.1 s-1, assuming a cytosolic protein concentration of 50 mg/ml), and the Km values of the activities for their respective inositol phosphate substrates (in the presence of 5 mM-ATP) were 1.6 microM, 3.8 microM and 1.4 microM. At least two forms of myo-inositol pentakisphosphate kinase activity could be resolved from a slime-mould cytosolic fraction by both pharmacological and chromatographic criteria. Rat brain cytosol and a soluble fraction derived from germinating mung-bean seedlings could phosphorylate myo-inositol D/L-1,2,4,5,6-, D/L-1,2,3,4,5-, 1,2,3,4,6- and 1,3,4,5,6-pentakisphosphates to myo-inositol hexakisphosphate: the relative first-order rate constants were 57:27:77:1 respectively for brain cytosol (with first-order rate constants in the intact cell of 0.0041, 0.0019, 0.0056 and 0.000073 s-1 respectively, assuming a cytosolic protein concentration of 50 mg/ml) and 1:11:12:33 respectively for mung-bean cytosol (with first-order rate constants in a supernatant fraction with a protein concentration of 10 mg/ml of 0.0002, 0.0022, 0.0024 and 0.0066 s-1 respectively).
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Lamosa, Pedro, Lu�s G. Gon�alves, Marta V. Rodrigues, L�gia O. Martins, Neil D. H. Raven i Helena Santos. "Occurrence of 1-Glyceryl-1-myo-Inosityl Phosphate in Hyperthermophiles". Applied and Environmental Microbiology 72, nr 9 (wrzesień 2006): 6169–73. http://dx.doi.org/10.1128/aem.00852-06.
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ABSTRACT The accumulation of compatible solutes was studied in the hyperthermophilic bacterium Aquifex pyrophilus as a function of the temperature and the NaCl concentration of the growth medium. Nuclear magnetic resonance analysis of cell extracts revealed the presence of α- and β-glutamate, di-mannosyl-di-myo-inositol phosphate, di-myo-inositol phosphate, and an additional compound here identified as 1-glyceryl-1-myo-inosityl phosphate. All solutes accumulated by A. pyrophilus are negatively charged at physiological pH. The intracellular levels of di-myo-inositol phosphate increased in response to supraoptimal growth temperature, while α- and β-glutamate accumulated in response to osmotic stress, especially at growth temperatures below the optimum. The newly discovered compound, 1-glyceryl-1-myo-inosityl phosphate, appears to play a double role in osmo- and thermoprotection, since its intracellular pool increased primarily in response to a combination of osmotic and heat stresses. This work also uncovered the nature of the unknown compound, previously detected in Archaeoglobus fulgidus (L. O. Martins et al., Appl. Environ. Microbiol. 63:896-902, 1997). The curious structural relationship between diglycerol phosphate (found only in Archaeoglobus species), di-myo-inositol phosphate (a canonical solute of hyperthermophiles), and the newly identified solute is highlighted. This is the first report on the occurrence of 1-glyceryl-1-myo-inosityl phosphate in living systems.
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Offer, J., J. C. Metcalfe i G. A. Smith. "The uptake of 3H-labelled monodeoxyfluoro-myo-inositols into thymocytes and their incorporation into phospholipid in permeabilized cells". Biochemical Journal 291, nr 2 (15.04.1993): 553–60. http://dx.doi.org/10.1042/bj2910553.
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Monodeoxyfluoro-myo-inositols were applied to electropermeabilized and intact thymocyte preparations to study their metabolism and uptake in order to investigate their suitability as potential inhibitors of phosphoinositide-mediated cellular responses. Only three of the monodeoxyfluoro-myo-inositols were incorporated into the phospholipids of thymocytes: 1D-3-deoxy-3-fluoro-myo-inositol, 5-deoxy-5-fluoro-myo-inositol and 1D-6-deoxy-6-fluoro-myo-inositol, all of which were weaker substrates for phosphatidylinositol synthase than was myo-inositol. The 3-, 5- and 6-fluoro analogues also behaved as competitive inhibitors, with K1 values of 350 +/- 5 microM, 350 +/- 5 microM and 2.9 +/- 2 mM respectively, compared with a Km for myo-inositol of 31 +/- 4 microM. When incubated with electropermeabilized thymocyte preparations, these three analogues of myo-inositol all formed phospholipids with chromatographic properties which corresponded to those of substituted phosphatidylinositol and phosphatidylinositol monophosphate. The uptake of myo-inositol and of the monodeoxyfluoro-myo-inositols into intact thymocytes was studied by a dual-label technique. All the monodeoxyfluoro-myo-inositols were taken up to some extent, but only 2-deoxy-2-fluoro-myo-inositol and 1D-3-deoxy-3-fluoro-myo-inositol were actively concentrated. The monodeoxyfluoro-myo-inositols were also assayed for their ability to inhibit the uptake of myo-inositol into cells. Both 2-deoxy-2-fluoro-myo-inositol and 1D-3-deoxy-3-fluoro-myo-inositol were effective inhibitors of myo-inositol uptake. Furthermore, 1D-1-deoxy-1-fluoro-myo-inositol, which was not taken up actively, was an effective inhibitor of myo-inositol uptake. The three effective inhibitors all showed Ki values of approximately 150 microM, close to the apparent Km for inositol uptake of 180 microM, and the 4-, 5- and 6-fluoro analogues had Ki values in excess of 10 mM.
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deSolms, S. Jane, Joseph P. Vacca i Joel R. Huff. "The total synthesis of (±)-myo-inositol-1,3,4-trisphosphate, (±)-myo-inositol-2,4,5-trisphosphate and (±)-myo-inositol-1,3,4,5-tetrakisphosphate". Tetrahedron Letters 28, nr 39 (styczeń 1987): 4503–6. http://dx.doi.org/10.1016/s0040-4039(00)96548-1.
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Biffen, M., i D. E. Hanke. "Reduction in the level of intracellular myo-inositol in cultured soybean (Glycine max) cells inhibits cell division". Biochemical Journal 265, nr 3 (1.02.1990): 809–14. http://dx.doi.org/10.1042/bj2650809.
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Although myo-inositol is included in media for the successful growth of plant tissues, the actual requirement of most tissues, including soybean (Glycine max) callus in suspension culture, for myo-inositol has not been demonstrated. We have made use of deoxyglucose to reduce intracellular levels of myo-inositol. Deoxyglucose is phosphorylated to deoxyglucose 6-phosphate, which inhibits L-myo-inositol 1-phosphate synthase, an important enzyme in the synthesis of myo-inositol. Addition of deoxyglucose to the medium resulted in a decrease in the intracellular level of myo-inositol that corresponded with a decrease in cell division. Cell viability was not affected. When myo-inositol was added to cells along with deoxyglucose, cell division was restored, as were intracellular levels of myo-inositol. Addition of myo-inositol had no affect on the uptake or metabolism of deoxyglucose. From these results we propose that myo-inositol has a role in maintaining cell division in soybean callus tissue in suspension culture.
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Martin, K. L., i T. K. Smith. "The myo-inositol-1-phosphate synthase gene is essential in Trypanosoma brucei". Biochemical Society Transactions 33, nr 5 (26.10.2005): 983–85. http://dx.doi.org/10.1042/bst0330983.
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The de novo synthesis of myo-inositol occurs via a two-step process: first, glucose 6-phosphate is converted into inositol 1-phosphate by an INO1 (myo-inositol-1-phosphate synthase; EC 5.5.1.4); then, it is dephosphorylated by an inositol monophosphatase. The myo-inositol can then be incorporated into PI (phosphatidylinositol), which is utilized in a variety of cellular functions, including the biosynthesis of GPI (glycosylphosphatidylinositol) anchors. A putative INO1 was identified in the Trypanosoma brucei genome database and, by recombinant expression in Escherichia coli, was shown to be a catalytically active INO1. To investigate the importance of INO1, we created a conditional knockout, which, under non-permissive conditions, showed that INO1 is an essential gene in bloodstream form T. brucei and that the de novo synthesized myo-inositol is used for the formation of PI and GPI anchors.
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SIU, TEVA, i GREGORY A. AHEARN. "Inositol Transport by Hepatopancreatic Brush-Border Membrane Vesicles of the Lobster Homarus Americanus". Journal of Experimental Biology 140, nr 1 (1.11.1988): 107–21. http://dx.doi.org/10.1242/jeb.140.1.107.
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The mechanism of [3H]myo-inositol transport by the lobster hepatopancreas was examined using purified brush-border membrane vesicles. Transport was stimulated by a 100 mmoll−1 inward Na+ gradient, but other cation gradients were ineffective, suggesting a Na+-dependent transfer mechanism. The transport system was most efficient at pH7.0 (both sides), rather than in the presence of a pH gradient (pHin = 7.0; pHout = 5.5) or at bilaterally low pH (pHin = pHout = 5.5). The system was shown to be electrogenic in two different ways. First, myo-inositol uptake was stimulated by anions of increasing permeability (SCN− > Cl− > gluconate). Second, an outwardly directed, valinomycin-induced K+ diffusion potential (inside negative) enhanced uptake in comparison with vesicles lacking the ionophore. Myo-inositol was transported by a carrier mechanism with an apparent Kt of 0.79mmoll−1, a Jmax of 6.3pmolmg protein−1 s−1, and by apparent diffusion with a permeability coefficient of 5.92 pmolmg protein−1s−1 (mmolT1)−1. D-Glucose was a noncompetitive inhibitor of myo-inositol uptake, but myo-inositol did not significantly reduce the transport of D-[3H]glucose. Vesicles preloaded with myo-inositol trans-stimulated [3H]myo-inositol uptake, whereas those preloaded with D-glucose did not, suggesting that the inositol carrier did not transport D-glucose. It is proposed that myo-inositol does not share the glucose carrier, and that D-glucose may modulateinositol influx by binding to a ‘regulator’ site on the inositol carrier.
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Nagata, Katsumi, Naohiro Hori, Kenzo Sato, Kunimasa Ohta, Hideaki Tanaka i Yasutake Hiji. "Cloning and functional expression of an SGLT-1-like protein from the Xenopus laevisintestine". American Journal of Physiology-Gastrointestinal and Liver Physiology 276, nr 5 (1.05.1999): G1251—G1259. http://dx.doi.org/10.1152/ajpgi.1999.276.5.g1251.
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A cDNA encoding an Na+-glucose cotransporter type 1 (SGLT-1)-like protein was cloned from the Xenopus laevis intestine by the 5′- and 3′-rapid amplification of cDNA ends method. The deduced amino acid sequence was 673 residues long, with a predicted mass of 74.1 kDa and 52–53% identity to mammalian SGLT-1s. This gene was expressed in the small intestine and kidney, reflecting a tissue distribution similar to that of SGLT-1. The function of the protein was studied using the two-microelectrode voltage-clamp technique after injection of cRNA into Xenopus laevis oocytes. Perfusion with myo-inositol elicited about twofold larger inward currents than perfusion withd-glucose. The order of the substrate specificity was myo-inositol > d-glucose >d-galactose ≥ α-methyl-d-glucoside. The current induced by myo-inositol increased with membrane hyperpolarization and depended on external myo-inositol and Na+: the apparent Michaelis-Menten constant was 0.25 ± 0.07 (SD) mM with myo-inositol, whereas the apparent concentration for half-maximal activation was 12.5 ± 1.0 mM and the Hill coefficient was 1.6 ± 0.1 with Na+. In conclusion, the cloned protein shares features with both SGLT-1 and the Na+- myo-inositol cotransporter.
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Borges, Nuno, Luís G. Gonçalves, Marta V. Rodrigues, Filipa Siopa, Rita Ventura, Christopher Maycock, Pedro Lamosa i Helena Santos. "Biosynthetic Pathways of Inositol and Glycerol Phosphodiesters Used by the Hyperthermophile Archaeoglobus fulgidus in Stress Adaptation". Journal of Bacteriology 188, nr 23 (6.10.2006): 8128–35. http://dx.doi.org/10.1128/jb.01129-06.
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ABSTRACT Archaeoglobus fulgidus accumulates di-myo-inositol phosphate (DIP) and diglycerol phosphate (DGP) in response to heat and osmotic stresses, respectively, and the level of glycero-phospho-myo-inositol (GPI) increases primarily when the two stresses are combined. In this work, the pathways for the biosynthesis of these three compatible solutes were established based on the detection of the relevant enzymatic activities and characterization of the intermediate metabolites by nuclear magnetic resonance analysis. The synthesis of DIP proceeds from glucose-6-phosphate via four steps: (i) glucose-6-phosphate was converted into l-myo-inositol 1-phosphate by l-myo-inositol 1-phosphate synthase; (ii) l-myo-inositol 1-phosphate was activated to CDP-inositol at the expense of CTP; this is the first demonstration of CDP-inositol synthesis in a biological system; (iii) CDP-inositol was coupled with l-myo-inositol 1-phosphate to yield a phosphorylated intermediate, 1,1′-di-myo-inosityl phosphate 3-phosphate (DIPP); (iv) finally, DIPP was dephosphorylated into DIP by the action of a phosphatase. The synthesis of the two other polyol-phosphodiesters, DGP and GPI, proceeds via the condensation of CDP-glycerol with the respective phosphorylated polyol, glycerol 3-phosphate for DGP and l-myo-inositol 1-phosphate for GPI, yielding the respective phosphorylated intermediates, 1X,1′X-diglyceryl phosphate 3-phosphate (DGPP) and 1-(1X-glyceryl) myo-inosityl phosphate 3-phosphate (GPIP), which are subsequently dephosphorylated to form the final products. The results disclosed here represent an important step toward the elucidation of the regulatory mechanisms underlying the differential accumulation of these compounds in response to heat and osmotic stresses.
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Stephens, L. R., P. T. Hawkins, A. J. Morris i P. C. Downes. "l-myo-inositol 1,4,5,6-tetrakisphosphate (3-hydroxy)kinase". Biochemical Journal 249, nr 1 (1.01.1988): 283–92. http://dx.doi.org/10.1042/bj2490283.
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Homogenates of primary-cultured murine bone macrophages contain an enzyme capable of synthesizing myo-[3H]inositol pentakisphosphate from myo-[3H]inositol tetrakisphosphate fractions derived from myo-[3H]inositol-labelled mouse macrophages and chick erythrocytes. D-myo-inositol 1,3,4,5-tetrakis[32P]-phosphate present in the same incubations was not phosphorylated. Since the myo-[3H]inositol-labelled tetrakisphosphate fractions used as substrates consist of a mixture of L-myo-inositol 1,4,5,6-tetrakisphosphate (60-85%) and a periodate-resistant tetrakisphosphate(s) whose characteristics are consistent with those of D-myo-inositol 1,3,4,5-tetrakisphosphate (the preceding paper [Stephens, Hawkins, Carter, Chahwala, Morris, Whetton & Downes (1988) Biochem. J. 249, 271-282]), these data suggest the existence of a kinase that phosphorylates L-myo-inositol 1,4,5,6-tetrakisphosphate to give a myo-inositol pentakisphosphate. A similar activity was identified in homogenates of rat cerebrum, liver, heart and parotid gland. D-myo-Inositol 1,3,4,5-tetrakis[32P]phosphate in the same incubations was not a substrate. The activity was almost entirely soluble in all the tissues investigated and was found at its greatest specific activity in brain cytosol. The activity was purified 120-fold from a rat brain homogenate by (NH4)2SO4 fractionation and anion-exchange chromatography. The activity was clearly distinct from D-myo-inositol 1,4,5-trisphosphate (3-hydroxy)kinase. Incubation of this partially purified preparation with L-myo-[3H]inositol 1,4,5,6-tetrakisphosphate from chick erythrocytes and [gamma-32P]ATP resulted in the formation of L-myo-[3H]-inositol [1-32P]1,3,4,5,6-pentakisphosphate. The enzyme is therefore identified as an L-myo-inositol 1,4,5,6-tetrakisphosphate (3-hydroxy)kinase.
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Higgins, B. D., i M. T. Kane. "Inositol transport in mouse embryonic stem cells". Reproduction, Fertility and Development 17, nr 6 (2005): 633. http://dx.doi.org/10.1071/rd05021.
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The uptake of myo-inositol by mouse embryonic stem (ES) cells was measured using [2-3H]myo-inositol. Uptake of myo-inositol by ES cells occurred in a mainly saturable, sodium-, time- and temperature-dependent manner, which was inhibited by glucose, phloridzin and ouabain. Self inhibition by inositol was much greater than inhibition by glucose indicating that transport was not occurring via a sodium-dependent glucose transporter. Uptake rate was much greater than efflux rate indicating a mainly unidirectional transport mechanism. Estimated kinetics parameters for sodium-dependent inositol uptake were a Km of 65.1 ± 11.8 μ mol L−1 and a Vmax of 5.0 ± 0.59 pmol μ g protein−1 h−1. Inositol uptake was also sensitive to osmolality; uptake increased in response to incubation in hypertonic medium indicating a possible role for inositol as an osmolyte in ES cells. These characteristics indicate that myo-inositol transport in mouse ES cells occurs by a sodium-dependent myo-inositol transporter protein.
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NIGOU, Jérôme, i Gurdyal S. BESRA. "Characterization and regulation of inositol monophosphatase activity in Mycobacterium smegmatis". Biochemical Journal 361, nr 2 (8.01.2002): 385–90. http://dx.doi.org/10.1042/bj3610385.
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Mycobacterium tuberculosis and related members of the genus Mycobacterium contain a number of inositol-based lipids, such as phosphatidylinositol mannosides, lipomannan and lipoarabinomannan. The synthesis of phosphatidylinositol in M. smegmatis is essential for growth and myo-inositol is a key metabolite for mycobacteria. Little is known about the biosynthesis of inositol in mycobacteria and the only known de novo pathway for myo-inositol biosynthesis involves a two-step process. First, cyclization of glucose 6-phosphate to afford myo-inositol 1-phosphate via inositol-1-phosphate synthase and, secondly, dephosphorylation of myo-inositol 1-phosphate by inositol monophosphatase (IMP) to afford myo-inositol. The following report examines IMP activity in M. smegmatis extracts, with regard to pH dependence, bivalent cation re quirement, univalent cation inhibition, regulation by growth and carbon source. We show that IMP activity, which is optimal at the end of the exponential growth phase in Sauton's medium, is Mg2+-dependent. Moreover, IMP activity is inhibited by Li+ and Na+, with Li+ also being able to inhibit growth of M. smegmatis in vivo. This study represents a first step in the delineation of myo-inositol biosynthesis in mycobacteria.
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Duthu, Brigitte, Douraid Houalla i Robert Wolf. "Phosphoranylation de polyols: Voie d'accès aux phosphates d'intérêt biologique. I. Cas du myo-inositol". Canadian Journal of Chemistry 66, nr 12 (1.12.1988): 2965–74. http://dx.doi.org/10.1139/v88-461.
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An original method for the phosphorylation of an unprotected myo-inositol is described, which yields several myo-inositol phosphates at the same time. The reaction proceeds via a partial or complete phosphoranylation of the cyclitol by means of the aminobicyclophosphane 8, followed by oxidation of the resulting bicyclophosphoranes bearing a P—H bond and acid hydrolysis of the neutral phosphates thus formed. In the case of the tris-phosphoranylation we identified, among the HPLC fractions, the myo-inositol-1,2-(cycl)phosphate 22, the myo-inositol-1-phosphate 23, and the myo-inositol-2-phosphate 24.
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Groenen, Pascal M. W., Hans M. W. M. Merkus, Fred C. G. J. Sweep, Ron A. Wevers, Fokje S. M. Janssen i Régine P. M. Steegers-Theunissen. "Kinetics of myo-inositol loading in women of reproductive age". Annals of Clinical Biochemistry: International Journal of Laboratory Medicine 40, nr 1 (1.01.2003): 79–85. http://dx.doi.org/10.1258/000456303321016213.
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Background: Myo-inositol plays a key role in an important intracellular signalling pathway. A deranged myo-inositol metabolism has been associated with neural tube defects. A myo-inositol loading test was performed to investigate the kinetics in healthy women of reproductive age. Methods: Five healthy non-obese females {mean age (standard deviation: SD) 22·8 (2·2) years} were recruited at the University Medical Center Nijmegen. Blood samples were drawn fasting and at 20, 40, 60, 90, 180 and 270 min after ingestion of 100 mg/kg body weight of myo-inositol. Urine samples were collected before myo-inositol loading and at 180 and 270 min post-loading. Samples were analysed for serum myo-, epi- and scyllo-inositol and glucose concentrations by gas chromatography. Plasma insulin concentrations were determined by radio-immunoassay. Random intercept models were fitted to evaluate the data. Results: The estimated myo-inositol and scyllo-inositol concentrations both reached maximum values at 180 min post-loading, respectively: mean (SD) 101·5 (9·2) µmol/L and 1·09 (0·11) µmol/L. The estimated plasma insulin and serum glucose concentrations decreased slightly but significantly during the experiment: P < 0·0001 and P < 0·05, respectively. At 180 and 270 min post-loading, urinary myo-inositol concentrations were increased and urinary glucose concentrations were unchanged. Conclusions: Myo-inositol enters the bloodstream quickly after oral ingestion and a small amount of myo-inositol is converted to scyllo-inositol. The synthesis of glucose from myo-inositol could not be detected by serum measurements. These data can be used in further research into the association between myo-inositol and neural tube defects.
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Daniellou, Richard, Hongyan Zheng i David RJ Palmer. "Kinetics of the reaction catalyzed by inositol dehydrogenase from Bacillus subtilis and inhibition by fluorinated substrate analogs". Canadian Journal of Chemistry 84, nr 4 (1.04.2006): 522–27. http://dx.doi.org/10.1139/v06-033.
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Inositol dehydrogenase (EC 1.1.1.18) from Bacillus subtilis catalyzes the oxidation of myo-inositol to scyllo-inosose by transfer of the equatorial hydride of the substrate to NAD+. This is a key enzyme in the metabolism of myo-inositol, a primary carbon source for soil bacteria. In light of our recent discovery that the enzyme has a broad substrate spectrum while maintaining high stereoselectivity, we seek a more thorough understanding of the enzyme and its active site. We have examined the kinetics of the recombinant enzyme, and synthesized fluorinated substrate analogues as competitive inhibitors. We have evaluated all rate constants in the ordered, sequential Bi Bi mechanism. No steady-state kinetic isotope effect is observed using myo-[2-2H]-inositol, indicating that the chemical step of the reaction is not rate-limiting. We have synthesized the substrate analogs 2-deoxy-2-fluoro-myo-inositol, its equatorial analog 1-deoxy-1-fluoro-scyllo-inositol, the gem-difluorinated analog 1-deoxy-1,1-difluoro-scyllo-inositol, and the sugar analog α-D-glucosyl fluoride. Of these, 1-deoxy-1-fluoro-scyllo-inositol showed no inhibition, while all others tested had Ki values comparable to the Km values of the analogous substrates myo-inositol and α-D-glucose.Key words: inositol dehydrogenase, enzyme mechanism, kinetics, competitive inhibitor, substrate analogue.
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Watkins, Oliver C., Mohammed Omedul Islam, Preben Selvam, Reshma Appukuttan Pillai, Amaury Cazenave-Gassiot, Anne K. Bendt, Neerja Karnani i in. "Myo-inositol alters 13C-labeled fatty acid metabolism in human placental explants". Journal of Endocrinology 243, nr 1 (październik 2019): 73–84. http://dx.doi.org/10.1530/joe-19-0267.
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We postulate that myo-inositol, a proposed intervention for gestational diabetes, affects transplacental lipid supply to the fetus. We investigated the effect of myo-inositol on fatty acid processing in human placental explants from uncomplicated pregnancies. Explants were incubated with 13C-labeled palmitic acid, 13C-oleic acid and 13C-docosahexaenoic acid across a range of myo-inositol concentrations for 24 h and 48 h. The incorporation of labeled fatty acids into individual lipids was quantified by liquid chromatography mass spectrometry. At 24 h, myo-inositol increased the amount of 13C-palmitic acid and 13C-oleic-acid labeled lipids (median fold change relative to control = 1). Significant effects were seen with 30 µM myo-inositol (physiological) for 13C-palmitic acid-lysophosphatidylcholines (1.26) and 13C-palmitic acid-phosphatidylethanolamines (1.17). At 48 h, myo-inositol addition increased 13C-oleic-acid-lipids but decreased 13C-palmitic acid and 13C-docosahexaenoic-acid lipids. Significant effects were seen with 30 µM myo-inositol for 13C-oleic-acid-phosphatidylcholines (1.25), 13C-oleic-acid-phosphatidylethanolamines (1.37) and 13C-oleic-acid-triacylglycerols (1.32) and with 100 µM myo-inositol for 13C-docosahexaenoic-acid-triacylglycerols (0.78). Lipids labeled with the same 13C-fatty acid showed similar responses when tested at the same time point, suggesting myo-inositol alters upstream processes such as fatty acid uptake or activation. Myo-inositol supplementation may alter placental lipid physiology with unknown clinical consequences.
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Raboy, Victor. "myo-Inositol-1,2,3,4,5,6-hexakisphosphate". Phytochemistry 64, nr 6 (listopad 2003): 1033–43. http://dx.doi.org/10.1016/s0031-9422(03)00446-1.
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DURMAZ, Yaşar, i Gökhun Çağatay ERBİL. "Effects of myo-inositol concentration on growth and pigments of Nannochloropsis oculata culture". Ege Journal of Fisheries and Aquatic Sciences 37, nr 2 (15.06.2020): 195–99. http://dx.doi.org/10.12714/egejfas.37.2.11.
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Inositols are used as growth promoting agents over plants. But microalgae are different from higher plant especially photosynthetic efficiency and productivity. According to the results of this study, myo-inositol addition to the culture medium of Nannochloropsis oculata provides higher cell densities. 100 mg L-1 myo-inositol added experimental group was reached to 1.42 fold cell mL-1, while the 500 mg L-1 myo-inositol added group was reached to 1.28 fold cell mL-1 than the control group. Mean chlorophyll a per cell amounts were calculated for experimental groups and control groups as 0.052 pg cell-1 and 0.053 pg cell-1, respectively. Mean total carotene per cell amounts were calculated for all groups as 0.016 pg cell-1. These results show that no difference was occurred between all groups by chlorophyll a and total carotene amounts per cell. This study shows that myo-inositol use in microalgae production may provide higher yields.
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Majumder, Arun Lahiri, Margaret D. Johnson i Susan A. Henry. "1l-myo-Inositol-1-phosphate synthase". Biochimica et Biophysica Acta (BBA) - Lipids and Lipid Metabolism 1348, nr 1-2 (wrzesień 1997): 245–56. http://dx.doi.org/10.1016/s0005-2760(97)00122-7.
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Jin, Jean Huaqian, i Andreas Seyfang. "High-affinity myo-inositol transport in Candida albicans: substrate specificity and pharmacology". Microbiology 149, nr 12 (1.12.2003): 3371–81. http://dx.doi.org/10.1099/mic.0.26644-0.
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Inositol is considered a growth factor in yeast cells and it plays an important role in Candida as an essential precursor for phospholipomannan, a glycophosphatidylinositol (GPI)-anchored glycolipid on the cell surface of Candida which is involved in the pathogenicity of this opportunistic fungus and which binds to and stimulates human macrophages. In addition, inositol plays an essential role in the phosphatidylinositol signal transduction pathway, which controls many cell cycle events. Here, high-affinity myo-inositol uptake in Candida albicans has been characterized, with an apparent K m value of 240±15 μM, which appears to be active and energy-dependent as revealed by inhibition with azide and protonophores (FCCP, dinitrophenol). Candida myo-inositol transport was sodium-independent but proton-coupled with an apparent K m value of 11·0±1·1 nM for H+, equal pH 7·96±0·05, suggesting that the C. albicans myo-inositol–H+ transporter is fully activated at physiological pH. C. albicans inositol transport was not affected by cytochalasin B, phloretin or phlorizin, an inhibitor of mammalian sodium-dependent inositol transport. Furthermore, myo-inositol transport showed high substrate specificity for inositol and was not significantly affected by hexose or pentose sugars as competitors, despite their structural similarity. Transport kinetics in the presence of eight different inositol isomers as competitors revealed that proton bonds between the C-2, C-3 and C-4 hydroxyl groups of myo-inositol and the transporter protein play a critical role for substrate recognition and binding. It is concluded that C. albicans myo-inositol–H+ transport differs kinetically and pharmacologically from the human sodium-dependent myo-inositol transport system and constitutes an attractive target for delivery of cytotoxic inositol analogues in this pathogenic fungus.
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Salamon´zyk, Grzegorz M., i K. Michał Pietrusiewicz. "A practical three-step conversion of myo-inositol into d-myo-inositol 1-phosphate". Tetrahedron Letters 32, nr 32 (sierpień 1991): 4031–32. http://dx.doi.org/10.1016/0040-4039(91)80619-h.
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Yi, Minghua, Liuzhen Yang, Jian Ma, Hang Liu, Min He, Chunyu Hu i Ping Yu. "Biosynthesis of myo-inositol in Escherichia coli by engineering myo-inositol-1-phosphate pathway". Biochemical Engineering Journal 164 (grudzień 2020): 107792. http://dx.doi.org/10.1016/j.bej.2020.107792.
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Krings, Eva, Karin Krumbach, Brigitte Bathe, Ralf Kelle, Volker F. Wendisch, Hermann Sahm i Lothar Eggeling. "Characterization of myo-Inositol Utilization by Corynebacterium glutamicum: the Stimulon, Identification of Transporters, and Influence on l-Lysine Formation". Journal of Bacteriology 188, nr 23 (22.09.2006): 8054–61. http://dx.doi.org/10.1128/jb.00935-06.
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ABSTRACT Although numerous bacteria possess genes annotated iol in their genomes, there have been very few studies on the possibly associated myo-inositol metabolism and its significance for the cell. We found that Corynebacterium glutamicum utilizes myo-inositol as a carbon and energy source, enabling proliferation with a high maximum rate of 0.35 h−1. Whole-genome DNA microarray analysis revealed that 31 genes respond to myo-inositol utilization, with 21 of them being localized in two clusters of >14 kb. A set of genomic mutations and functional studies yielded the result that some genes in the two clusters are redundant, and only cluster I is necessary for catabolizing the polyol. There are three genes which encode carriers belonging to the major facilitator superfamily and which exhibit a >12-fold increased mRNA level on myo-inositol. As revealed by mutant characterizations, one carrier is not involved in myo-inositol uptake whereas the other two are active and can completely replace each other with apparent Km s for myo-inositol as a substrate of 0.20 mM and 0.45 mM, respectively. Interestingly, upon utilization of myo-inositol, the l-lysine yield is 0.10 mol/mol, as opposed to 0.30 mol/mol, with glucose as the substrate. This is probably not only due to myo-inositol metabolism alone since a mixture of 187 mM glucose and 17 mM myo-inositol, where the polyol only contributes 8% of the total carbon, reduced the l-lysine yield by 29%. Moreover, genome comparisons with other bacteria highlight the core genes required for growth on myo-inositol, whose metabolism is still weakly defined.
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Dumschott, Kathryn, Julie Dechorgnat i Andrew Merchant. "Water Deficit Elicits a Transcriptional Response of Genes Governing d-pinitol Biosynthesis in Soybean (Glycine max)". International Journal of Molecular Sciences 20, nr 10 (15.05.2019): 2411. http://dx.doi.org/10.3390/ijms20102411.
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d-pinitol is the most commonly accumulated sugar alcohol in the Leguminosae family and has been observed to increase significantly in response to abiotic stress. While previous studies have identified genes involved in d-pinitol synthesis, no study has investigated transcript expression in planta. The present study quantified the expression of several genes involved in d-pinitol synthesis in different plant tissues and investigated the accumulation of d-pinitol, myo-inositol and other metabolites in response to a progressive soil drought in soybean (Glycine max). Expression of myo-inositol 1-phosphate synthase (INPS), the gene responsible for the conversion of glucose-6-phosphate to myo-inositol-1-phosphate, was significantly up regulated in response to a water deficit for the first two sampling weeks. Expression of myo-inositol O-methyl transferase (IMT1), the gene responsible for the conversion of myo-inositol into d-ononitol was only up regulated in stems at sampling week 3. Assessment of metabolites showed significant changes in their concentration in leaves and stems. d-Pinitol concentration was significantly higher in all organs sampled from water deficit plants for all three sampling weeks. In contrast, myo-inositol, had significantly lower concentrations in leaf samples despite up regulation of INPS suggesting the transcriptionally regulated flux of carbon through the myo-inositol pool is important during water deficit.
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Van Lookeren Campagne, M. M., C. Erneux, R. Van Eijk i P. J. M. Van Haastert. "Two dephosphorylation pathways of inositol 1,4,5-trisphosphate in homogenates of the cellular slime mould Dictyostelium discoideum". Biochemical Journal 254, nr 2 (1.09.1988): 343–50. http://dx.doi.org/10.1042/bj2540343.
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Dictyostelium discoideum homogenates contain phosphatase activity which rapidly dephosphorylates Ins(1,4,5)P3 (D-myo-inositol 1,4,5-trisphosphate) to Ins (myo-inositol). When assayed in Mg2+, Ins(1,4,5)P3 is dephosphorylated by the soluble Dictyostelium cell fraction to 20% Ins(1,4)P2 (D-myo-inositol 1,4-bisphosphate) and 80% Ins(4,5)P2 (D-myo-inositol 4,5-bisphosphate). In the particulate fraction Ins(1,4,5)P3 5-phosphatase is relatively more active than the Ins(1,4,5)P3 1-phosphatase. CaCl2 can replace MgCl2 only for the Ins(1,4,5)P3 5-phosphatase activity. Ins(1,4)P2 and Ins(4,5)P2 are both further dephosphorylated to Ins4P (D-myo-inositol 4-monophosphate), and ultimately to Ins. Li+ ions inhibit Ins(1,4,5)P3 1-phosphatase, Ins(1,4)P2 1-phosphatase, Ins4P phosphatase and L-Ins1P (L-myo-inositol 1-monophosphate) phosphatase activities; Ins(1,4,5)P3 1-phosphatase is 10-fold more sensitive to Li+ (half-maximal inhibition at about 0.25 mM) than are the other phosphatases (half-maximal inhibition at about 2.5 mM). Ins(1,4,5)P3 5-phosphatase activity is potently inhibited by 2,3-bisphosphoglycerate (half-maximal inhibition at 3 microM). Furthermore, 2,3-bisphosphoglycerate also inhibits dephosphorylation of Ins(4,5)P2. These characteristics point to a number of similarities between Dictyostelium phospho-inositol phosphatases and those from higher organisms. The presence of an hitherto undescribed Ins(1,4,5)P3 1-phosphatase, however, causes the formation of a different inositol bisphosphatase isomer [Ins(4,5)P2] from that found in higher organisms [Ins(1,4)P2]. The high sensitivity of some of these phosphatases for Li+ suggests that they may be the targets for Li+ during the alteration of cell pattern by Li+ in Dictyostelium.
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Yorek, Mark A., Joyce A. Dunlap, Michael J. Thomas, Patrick R. Cammarata, Cheng Zhou i William L. Lowe. "Effect of TNF-α on SMIT mRNA levels andmyo-inositol accumulation in cultured endothelial cells". American Journal of Physiology-Cell Physiology 274, nr 1 (1.01.1998): C58—C71. http://dx.doi.org/10.1152/ajpcell.1998.274.1.c58.
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Previously we have shown that hyperosmolarity increases Na+- myo-inositol cotransporter (SMIT) activity and mRNA levels in cultured endothelial cells. Because hyperosmolarity and cytokines, such as tumor necrosis factor-α (TNF-α), activate similar signal transduction pathways, we examined the effect of TNF-α on SMIT mRNA levels and myo-inositol accumulation. In contrast to the effect of hyperosmolarity, TNF-α caused a time- and concentration-dependent decrease in SMIT mRNA levels and myo-inositol accumulation. The effect of TNF-α on myo-inositol accumulation was found in large-vessel endothelial cells (derived from the aorta and pulmonary artery) and cerebral microvessel endothelial cells. In bovine aorta and bovine pulmonary artery endothelial cells, TNF-α activated nuclear factor (NF)-κB. TNF-α also increased ceramide levels, and C2-ceramide mimicked the effect of TNF-α on SMIT mRNA levels and myo-inositol accumulation in bovine aorta endothelial cells. Pyrrolidinedithiocarbamate, genistein, and 7-amino-1-chloro-3-tosylamido-2-hepatanone, compounds that can inhibit NF-κB activation, partially prevented the TNF-α-induced decrease in myo-inositol accumulation. The effect of TNF-α on myo-inositol accumulation was also partially prevented by the protein kinase C inhibitor calphostin C but not by staurosporine. These studies demonstrate that TNF-α causes a decrease in SMIT mRNA levels and myo-inositol accumulation in cultured endothelial cells, which may be related to the activation of NF-κB.
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Basu, Sautrik, Anusuya Basak, Dibyendu Sekhar Mahanty, Sayani Bhattacharjee i Jukta Adhikari. "Biosynthesis of Myo-Inositol in Chloroplasts of Salinity-Stressed Marine Macro Alga Ulva lactuca". Botanica 25, nr 1 (1.06.2019): 32–40. http://dx.doi.org/10.2478/botlit-2019-0004.
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AbstractThe present communication reports enhanced myo-inositol biosynthesis under natural conditions in Ulva lactuca Linn. based on the study conducted on its two prime enzymes [L-myo-inositol-1-phosphate synthase (MIPS) and myo-inositol-1-phosphate phosphatase (MIPP)] involved in myo-inositol biosynthesis. The two key enzymes obtained from chloroplastidial sources were partially purified to about 49- and 58-fold, respectively, over the homogenate following low speed centrifugation, high speed centrifugation, 0–80% ammonium sulphate precipitation and successive chromatography using ion exchange, gel filtration and molecular sieve packed columns. MIPS preparations specifically utilized D-glucose-6-phosphate and NAD as its exclusive substrate and coenzyme, while MIPP preparations used D/L-myo-inositol -1- phosphate as its principal substrate. Using non-linear regression kinetics method, the Km values of MIPS for G-6-P and NAD were calculated to be 2.6340 mM and 0.1271 mM, while the Km value of MIPP for D-MIP was recorded to be 0.02128 mM. Both enzymes were remarkably active within a temperature range of 20–40°C, and the optimum pH for both enzymes were found to be 7.5. Different cations and organic modifiers exhibited variable effects on the activity of both enzymes. The content of free myo-inositol was found to increase proportionately with the increase of surface salinity of the Chilika Lagoon, Odisha, India.
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Shears, S. B., D. J. Storey, A. J. Morris, A. B. Cubitt, J. B. Parry, R. H. Michell i C. J. Kirk. "Dephosphorylation of myo-inositol 1,4,5-trisphosphate and myo-inositol 1,3,4-triphosphate". Biochemical Journal 242, nr 2 (1.03.1987): 393–402. http://dx.doi.org/10.1042/bj2420393.
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We have augmented our previous studies [Storey, Shears, Kirk & Michell (1984) Nature (London) 312, 374-376] on the subcellular location and properties of Ins(1,4,5)P3 (inositol 1,4,5-trisphosphate) phosphatases in rat liver and human erythrocytes. We also investigate Ins(1,3,4)P3 (inositol 1,3,4-trisphosphate) metabolism by rat liver. Membrane-bound and cytosolic Ins(1,4,5)P3 phosphatases both attack the 5-phosphate. The membrane-bound enzyme is located on the inner face of the plasma membrane, and there is little or no activity associated with Golgi apparatus. Cytosolic Ins(1,4,5)P3 5-phosphatase (Mr 77,000) was separated by gel filtration from Ins(1,4)P2 (inositol 1,4-bisphosphate) and inositol 1-phosphate phosphatases (Mr 54,000). Ins(1,4,5)P3 5-phosphatase activity in hepatocytes was unaffected by treatment of the cells with insulin, vasopressin, glucagon or dibutyryl cyclic AMP. Ins(1,4,5)P3 5-phosphatase activity in cell homogenates was unaffected by changes in [Ca2+] from 0.1 to 2 microM. After centrifugation of a liver homogenate at 100,000 g, Ins(1,3,4)P3 phosphatase activity was largely confined to the supernatant. The sum of the activities in the supernatant and the pellet exceeded that in the original homogenate. When these fractions were recombined, Ins(1,3,4)P3 phosphatase activity was restored to that observed in unfractionated homogenate. Ins(1,3,4)P3 was produced from Ins(1,3,4,5)P4 (inositol 1,3,4,5-tetrakisphosphate) and was metabolized to a novel InsP2 that was the 3,4-isomer. Ins(1,3,4)P3 phosphatase activity was not changed by 50 mM-Li+ or 0.07 mM-Ins(1,4)P2 alone, but when added together these agents inhibited Ins(1,3,4)P3 metabolism. In Li+-treated and vasopressin-stimulated hepatocytes, Ins(1,4)P2 may reach concentrations sufficient to inhibit Ins(1,3,4)P3 metabolism, with little effect on Ins(1,4,5)P3 hydrolysis.
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Chen, Liangjing, Elias T. Spiliotis i Mary F. Roberts. "Biosynthesis of Di-myo-Inositol-1,1′-Phosphate, a Novel Osmolyte in Hyperthermophilic Archaea". Journal of Bacteriology 180, nr 15 (1.08.1998): 3785–92. http://dx.doi.org/10.1128/jb.180.15.3785-3792.1998.
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ABSTRACT Biosynthesis of di-myo-inositol-1,1′-phosphate (DIP) is proposed to occur with myo-inositol andmyo-inositol 1-phosphate (I-1-P) used as precursors. Activation of the I-1-P with CTP and condensation of the resultant CDP-inositol (CDP-I) with myo-inositol then generates DIP. The sole known biosynthetic pathway of inositol in all organisms is the conversion of d-glucose-6-phosphate tomyo-inositol. This conversion requires two key enzymes:l-I-1-P synthase and I-1-P phosphatase. Enzymatic assays using 31P nuclear magnetic resonance spectroscopy as well as a colorimetric assay for inorganic phosphate have confirmed the occurrence of l-I-1-P synthase and a moderately specific I-1-P phosphatase. The enzymatic reaction that couples CDP-I withmyo-inositol to generate DIP has also been detected inMethanococcus igneus. 13C labeling studies with [2,3-13C]pyruvate and [3-13C]pyruvate were used to examine this pathway in M. igneus. Label distribution in DIP was consistent with inositol units formed from glucose-6-phosphate, but the label in the glucose moiety was scrambled via transketolase and transaldolase activities of the pentose phosphate pathway.
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Nakanishi, T., A. Yamauchi, M. Sugita i Y. Takamitsu. "Aldose reductase and myo-inositol transporter mRNA are independently regulated in rat renal medulla." Journal of the American Society of Nephrology 7, nr 2 (luty 1996): 283–89. http://dx.doi.org/10.1681/asn.v72283.
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During antidiuresis, renal papillary cells accumulate organic osmolytes preferentially over inorganic ions. It has been previously demonstrated that sodium infusion increased all of these organic osmolytes except myo-inositol (1). Conversely, urea infusion increased only glycerophosphorylcholine significantly. In addition to sodium and urea, potassium localized in tissue and urine influenced the composition of organic osmolytes. The goal of this study was to clarify how the level of mRNA of osmoregulatory protein is regulated by the extracellular solutes and how it affects the accumulation of organic osmolytes. To clarify the relationship between intra- or extracellular solutes and the regulation of Na/myo-inositol cotransporter and aldose reductase, mRNA of these osmo-regulatory proteins were determined in water-deprived sodium chloride-, potassium chloride-, and urea-loaded rats. Medullary content of sorbitol and myo-inositol, and aldose-reductase enzymatic activity were measured simultaneously in these animals. In water-deprived, sodium-loaded, and potassium-loaded rats, the inner medullary sorbitol content increased significantly in accordance with the rise in the enzymatic activity and the level of aldose reductase mRNA. In urea-loaded rats, both the sorbitol content and the level of aldose reductase mRNA were equal to that in hydrated rats. In the outer and inner medullary tissues, the level of myo-inositol transporter mRNA was increased in all hyperosmolality protocols, including urea infusion, which corresponded with the rise in myo-inositol content. In conclusion, potassium chloride infusion is as effective as water deprivation and sodium chloride infusion in raising the level of aldose reductase and myo-inositol transporter mRNA, whereas urea influenced only myo-inositol transporter. Although aldose reductase and myo-inositol transporter are osmoregulatory proteins in the renal medulla, the levels of aldose reductase and sodium-dependent myo-inositol transporter mRNA are regulated independently.
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Dai, Zhijie, Sookja K. Chung, Dengshun Miao, Kam S. Lau, Alfred W. H. Chan i Annie W. C. Kung. "Sodium/myo-inositol cotransporter 1 and myo-inositol are essential for osteogenesis and bone formation". Bone 47 (październik 2010): S371. http://dx.doi.org/10.1016/j.bone.2010.09.119.
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Dai, Zhijie, Sookja K. Chung, Dengshun Miao, Kam S. Lau, Alfred WH Chan i Annie WC Kung. "Sodium/myo-inositol cotransporter 1 and myo-inositol are essential for osteogenesis and bone formation". Journal of Bone and Mineral Research 26, nr 3 (18.02.2011): 582–90. http://dx.doi.org/10.1002/jbmr.240.
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Gee, N. S., C. I. Ragan, K. J. Watling, S. Aspley, R. G. Jackson, G. G. Reid, D. Gani i J. K. Shute. "The purification and properties of myo-inositol monophosphatase from bovine brain". Biochemical Journal 249, nr 3 (1.02.1988): 883–89. http://dx.doi.org/10.1042/bj2490883.
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1. An inositol monophosphatase was purified to homogeneity from bovine brain. 2. The enzyme is a dimer of subunit Mr 29,000. 3. The enzyme hydrolyses both enantiomers of myo-inositol 1-phosphate and both enantiomers of myo-inositol 4-phosphate, but has no activity towards inositol bisphosphates, inositol trisphosphates or inositol 1,3,4,5-tetrakisphosphate. 4. Several non-inositol-containing monophosphates are also substrates. 5. The enzyme requires Mg2+ for activity, and Zn2+ supports activity to a small extent. 6. Other bivalent cations (including Zn2+) are inhibitors, competitive with Mg2+. 7. Phosphate, but not inositol, is an inhibitor competitive with substrate. 8. Li+ inhibits hydrolysis of inositol 1-phosphate and inositol 4-phosphate uncompetitively with different apparent Ki values (1.0 mM and 0.26 mM respectively).
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Strasser, Heiner, Christina Hoffmann, Hans Grisebach i Ulrich Matern. "Are Polyphosphoinositides Involved in Signal Transduction of Elicitor-Induced Phytoalexin Synthesis in Cultured Plant Cells ?" Zeitschrift für Naturforschung C 41, nr 7-8 (1.08.1986): 717–24. http://dx.doi.org/10.1515/znc-1986-7-810.
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Abstract The phospholipids of cultured parsley and soybean cells were labelled with myo-[2-3H]inositol, [2-3H]glycerol or [32P]orthophosphate. By one-and two-dimensional chromatographic comparison of the labelled phospholipids with reference substances, the presence of 1-(3-sn-phosphatidyl)-ᴅ-myo-inositol 4-phosphate and 1-(3-sn-phosphatidyl)-ᴅ-myo-inositol 4,5-bisphosphate was demonstrated in these cultures. These results were corroborated by analysis of the deacylation products. Cells were labelled with either myo-[2-3H]inositol, [2-3H]glycerol or [32P]orthophosphate and subsequently challenged with elicitor for various lengths of time. Radioactivity in individual phosphoinositides from these cells was determined. No significant influence of elicitor-challenge of either soybean or parsley cells on incorporation of 3H or 32P into polyphosphoinositides was found between 0.5 and 20 min after elicitor addition.
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J. Garegg, P. "Synthesis of 1?- and 1?-4-O-benzyl-myo-inositol, 1?-4-O-α-?-fucopyranosyl-myo-inositol (identical to a natural glycoside), and 1?-4-O-α-?-fucopyranosyl-myo-inositol". Carbohydrate Research 139, nr 1 (5.06.1985): 209–15. http://dx.doi.org/10.1016/0008-6215(85)85086-2.
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Klages, Karin, Helen Donnison, Helen Boldingh i Elspeth MacRae. "myo-Inositol is the major sugar in Actinidia arguta during early fruit development". Functional Plant Biology 25, nr 1 (1998): 61. http://dx.doi.org/10.1071/pp97052.
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Actinidia arguta (Sieb. et Zucc.) Planch. ex Miq. is a cold tolerant and heavy cropping species from the kiwifruit [Actinidia deliciosa var. deliciosa (A. Chev.) C.F. Liang et A.R.Ferguson] family that has potential for commercialisation. As fruit developed, glucose was the major sugar (74%) in A. deliciosa during the first 40 days after anthesis, whereas myo-inositol was the major sugar (60–65%) in A. arguta.myo-Inositol accumulated rapidly in A. arguta during the first 20–30 daa then more slowly as fruit grew to reach a steady state level, between 15 and 50 mg fruit-1 for different selections. Peak levels were 55-60 mg g-1 dry wt. In contrast, maximum myo-inositol concentrations in A. deliciosa were only 18 mg g-1 dry wt. As fruit of A. arguta ripened, sucrose became the dominant sugar. In contrast to the fruit, myo-inositol concentrations were lower in leaves of A. arguta(~5 mg g-1 dry wt; ~10% of major sugars) than in leaves of A. deliciosa (15 mg g-1 dry wt; ~20% of major sugars). To ascertain whether myo-inositol was transported from the leaves to the fruit in the phloem stream, exudates were also analysed. In both species, sucrose was the predominant sugar (>95%) in the phloem. Therefore we suggest that an unusual accumulation of myo-inositol in A. arguta during early stages of fruit development, may be due to synthesis in the fruit.
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ARNER, Ryan J., K. Sandeep PRABHU, Jerry T. THOMPSON, George R. HILDENBRANDT, Andrew D. LIKEN i C. Channa REDDY. "myo-Inositol oxygenase: molecular cloning and expression of a unique enzyme that oxidizes myo-inositol and d-chiro-inositol". Biochemical Journal 360, nr 2 (26.11.2001): 313–20. http://dx.doi.org/10.1042/bj3600313.
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myo-Inositol oxygenase (MIOX) catalyses the first committed step in the only pathway of myo-inositol catabolism, which occurs predominantly in the kidney. The enzyme is a non-haem-iron enzyme that catalyses the ring cleavage of myo-inositol with the incorporation of a single atom of oxygen. A full-length cDNA was isolated from a pig kidney library with an open reading frame of 849bp and a corresponding protein subunit molecular mass of 32.7kDa. The cDNA was expressed in a bacterial pET expression system and an active recombinant MIOX was purified from bacterial lysates to electrophoretic homogeneity. The purified enzyme displayed the same catalytic properties as the native enzyme with Km and kcat values of 5.9mM and 11min−1 respectively. The pI was estimated to be 4.5. Preincubation with 1mM Fe2+ and 2mM cysteine was essential for the enzyme's activity. d-chiro-Inositol, a myo-inositol isomer, is a substrate for the recombinant MIOX with an estimated Km of 33.5mM. Both myo-inositol and d-chiro-inositol have been implicated in the pathogenesis of diabetes. Thus an understanding of the regulation of MIOX expression clearly represents a potential window on the aetiology of diabetes as well as on the control of various intracellular phosphoinositides and key signalling pathways.
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Nakanishi, T., i M. B. Burg. "Osmoregulatory fluxes of myo-inositol and betaine in renal cells". American Journal of Physiology-Cell Physiology 257, nr 5 (1.11.1989): C964—C970. http://dx.doi.org/10.1152/ajpcell.1989.257.5.c964.
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Renal medullary cells contain high concentrations of "compatible" organic osmolytes, such as myo-inositol, betaine, sorbitol, and glycero-phosphorylcholine. These organic osmolytes accumulate as an osmoregulatory response to the high and variable interstitial NaCl concentration that is part of the urinary concentrating mechanism. Madin-Darby canine kidney (MDCK) cells in culture were previously shown to accumulate myo-inositol and betaine in response to increased NaCl. These organic osmolytes are taken up by sodium-dependent active transport into the cells from the medium. The maximum concentration is not reached until 2-4 days after an increase in medium osmolality. The purpose of this study was to characterize the response to a decrease in medium osmolality of cells that had been grown at a high osmolality. The initial response to decreased osmolality was a rapid, transient efflux of both myo-inositol and betaine from the cells. Efflux was greatest during the first 15 min and resulted in a reduction of cell myo-inositol and betaine by almost 13 and 22%, respectively, after 3 h. Active myo-inositol and betaine influx fell more slowly, reaching a lower limit after approximately 1-2 days. The reduced influx was followed by progressive decrease in cell myo-inositol and betaine to approximately 30% of the initial value after 6 days. Thus, after a decrease in medium osmolality, MDCK cell myo-inositol and betaine fell because of a rapid, transient increase in efflux and a slow, sustained decrease in active influx.
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Rolnik, Agata, Beata Olas, Joanna Szablińska-Piernik, Lesław Bernard Lahuta, Andrzej Rynkiewicz, Piotr Cygański, Katarzyna Socha, Leszek Gromadziński, Michael Thoene i Michał Majewski. "Beneficial In Vitro Effects of a Low Myo-Inositol Dose in the Regulation of Vascular Resistance and Protein Peroxidation under Inflammatory Conditions". Nutrients 14, nr 5 (7.03.2022): 1118. http://dx.doi.org/10.3390/nu14051118.
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Oxidative stress induces functional changes in arteries. Therefore, the effect of myo-inositol, a possible anti-inflammatory/antioxidant agent was studied on human plasma and rat thoracic arteries. Aortic rings from male Wistar rats (3 months of age) were incubated with myo-inositol (1, 10 and 100 μM, 120 min) and analyzed using the gas chromatography (GC) method. In another experiment, aortic rings were protected first with myo-inositol (1 µM, 60 min) and then subjected to a thromboxane receptor agonist (U-46619, 0.1 nM, 60 min). Therefore, these four groups under the following conditions were studied: (i) the control in the vehicle; (ii) myo-inositol; (iii) the vehicle plus U-46619; (iv) myo-inositol plus U-46619. The hemostatic parameters of human plasma and an H2O2/Fe2+ challenge for lipid and protein peroxidation were also performed. Myo-inositol was not absorbed into the pre-incubated aortic rings as measured by the GC method (0.040 µg/mg, p ≥ 0.8688). The effect of myo-inositol was more significant in the impaired arteries due to U-46619 incubation, which resulted in an improved response to acetylcholine (% Emax: 58.47 vs. 86.69), sodium nitroprusside (logEC50: −7.478 vs. −8.076), CORM-2 (% Emax: 44.08 vs. 83.29), pinacidil (logEC50: −6.489 vs. −6.988) and noradrenaline (logEC50: −7.264 vs. −6.525). This was most likely a possible response to increased nitric oxide release (×2.6-fold, p < 0001), and decreased hydrogen peroxide production (×0.7-fold, p = 0.0012). KCl-induced membrane depolarization was not modified (p ≥ 0.4768). Both the plasma protein carbonylation (×0.7-fold, p = 0.0006), and the level of thiol groups (×3.2-fold, p = 0.0462) were also improved, which was not significant for TBARS (×0.8-fold, p = 0.0872). The hemostatic parameters were also not modified (p ≥ 0.8171). A protective effect of myo-inositol was demonstrated against prooxidant damage to human plasma and rat thoracic arteries, suggesting a strong role of this nutraceutical agent on vasculature which may be of benefit against harmful environmental effects.
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LAUSSMANN, Tim, Komandla Malla REDDY, K. Kishta REDDY, J. R. FALCK i Günter VOGEL. "Diphospho-myo-inositol phosphates from Dictyostelium identified as d-6-diphospho-myo-inositol pentakisphosphate and d-5,6-bisdiphospho-myo-inositol tetrakisphosphate". Biochemical Journal 322, nr 1 (15.02.1997): 31–33. http://dx.doi.org/10.1042/bj3220031.
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Two diphospho-myo-inositol phosphates from Dictyostelium were recently investigated by two-dimensional 1H/31P NMR analysis and assigned to be either d-4-diphospho-myo-inositol pentakisphosphate (d-4-PP-InsP5) and d-4,5-bisdiphospho-myo-inositol tetrakisphosphate (d-4,5-bis-PP-InsP4) or their corresponding enantiomers d-6-PP-InsP5 and d-5,6-bis-PP-InsP4. In the present study the naturally occurring enantiomers were identified by using defined synthetic PP-InsP5 isomers as substrates for a partially purified PP-InsP5 5-kinase from Dictyostelium. This enzyme specifically phosphorylates the naturally occurring PP-InsP5 and the synthetic d-6-PP-InsP5, leading to d-5,6-bis-PP-InsP4. In contrast, neither d-4-PP-InsP5 nor d-1-PP-InsP5 or d-3-PP-InsP5 are converted by the enzyme.
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Ellingson, David, Ted Pritchard, Pamela Foy, Kathryn King, Barbara Mitchell, John Austad, Doug Winters i Darryl Sullivan. "Analysis of Free and Total Myo-Inositol in Foods, Feeds, and Infant Formula by High-Performance Anion Exchange Chromatography with Pulsed Amperometric Detection, Including a Novel Total Extraction Using Microwave-Assisted Acid Hydrolysis and Enzymatic Treatment". Journal of AOAC INTERNATIONAL 95, nr 5 (1.09.2012): 1469–78. http://dx.doi.org/10.5740/jaoacint.12-028.
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Abstract A method for the analysis of free and total myo-inositol in foods, feeds, and infant formulas has been developed and validated using high-performance anion exchange chromatography with pulsed amperometric detection. The option of a free myo-inositol determination or a complete total myo-inositol determination from main bound sources can be achieved. These sources include phytates, lower phosphorylated forms, and phosphatidylinositol. This approach gives the option for subtraction of myo-inositol from nonbioavailable sources when it is quantified using other methods if a total bioavailable myo-inositol result is desired for nutritional labeling of a product. The free analysis was validated in a milk-based infant formula, giving RSDR of 2.29% and RSDr of 2.06%. A mean recovery of 97.9% was achieved from various spike levels of myo-inositol. Certified National Institute of Standards and Technology reference material verified the method's compatibility and specificity. Two different total analyses were validated in a soy-based infant formula and compared. One technique involved using a conventional acid hydrolysis with autoclave incubation for 6 h, while the other used a novel technique of microwave-assisted acid hydrolysis with enzymatic treatment that can minimize extraction to 1 day. The autoclave analysis had RSDR of 2.08% and RSDr of 1.55%, along with a mean spike recovery of 102.1% at various myo-inositol spike levels. The microwave/enzyme total analysis had RSDR of 4.34% and RSDr of 4.70%, along with a mean spike recovery of 104.2% at various spike levels of myo-inositol. Main sources of myo-inositol including phytic acid and phosphatidylinositol were tested with both total analyses. Mean recoveries of phytic acid and phosphatidylinositol through the autoclave total analysis were 90.4 and 98.3%, respectively. Mean spike recoveries for these same sources in soy-based infant formula through the microwave/enzyme total analysis were 97.2 and 96.3%, respectively. Comparison of soy-based infant formula and corn grain samples with high levels of these main sources showed in similar results, indicating both total analyses are acceptable for use. An additional glycerol kinase step was also developed to remove glycerol from the chromatographic elution window of myo-inositol in samples with high levels of glycerol.
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Simmons, D., J. Bomford i L. L. Ng. "myo-Inositol influx into human leucocytes: methods of measurement and the effect of glucose". Clinical Science 78, nr 3 (1.03.1990): 335–41. http://dx.doi.org/10.1042/cs0780335.
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1. Low intracellular concentrations of myo-inositol in diabetic cells may contribute to the development of tissue damage. The cause of these low levels is unknown, but inhibition of a putative myo-inositol transporter by high concentrations of glucose has been proposed. We have developed a triple-isotope method for estimating myo-inositol influx into human leucocytes and so investigated both the kinetics of this uptake in normal volunteers and the effect of glucose upon it. 2. Uptake was composed of a passive component with a rate constant of 2.4 ± 0.3 × 10−2 min−1 and a saturable component with a Km of 61 ± 23 μmol/l and a Vmax. of 11.3 ± 4.5 × 10−4 mmol min−1 l−1. Ouabain and low extracellular concentrations of sodium partly inhibited influx. Uptake was predominantly into the cytosolic fraction of the cell with 12% entering the membrane-associated fraction at both 5 and 10 min. 3. myo-inositol influx was significantly inhibited by both d- and l-glucose but not by sucrose. Neither cytochalasin B nor ethyl isopropyl amiloride significantly inhibited uptake. 4. It is concluded that a myo-inositol transporter exists in human leucocytes which is similar to that found in other species and tissues. Our technique allows myoinositol influx in diabetic subjects to be related to varying glycaemic control and tissue damage.
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Attwood, P. V., J. B. Ducep i M. C. Chanal. "Purification and properties of myo-inositol-1-phosphatase from bovine brain". Biochemical Journal 253, nr 2 (15.07.1988): 387–94. http://dx.doi.org/10.1042/bj2530387.
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myo-Inositol-1-phosphatase from bovine brain was purified over 2000-fold. The native enzyme has a Mr of 59,000, and on SDS/polyacrylamide-gel electrophoresis the subunit Mr was 31,000. Thus the native enzyme is a dimer of two apparently identical subunits. The enzyme, purified to a specific activity of more than 300 units/mg of protein (1 unit of enzyme activity corresponds to the release of 1 mumol of Pi/h at 37 degrees C), catalysed the hydrolysis of a variety of phosphorylated compounds, the best one, in terms of V/Km, being D-myo-inositol 1-phosphate. Kinetic constants of compounds tested, including both isomers of glycerophosphate and two deoxy forms of beta-glycerophosphate, were measured. They show the importance of the two hydroxyl groups which are adjacent to the phosphate in myo-inositol 1-phosphate. With a wide variety of substrates Li+ was found to be an uncompetitive inhibitor whose Ki varied with substrate structure.
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Faraci, W. S., S. H. Zorn, A. V. Bakker, E. Jackson i K. Pratt. "Beryllium competitively inhibits brain myo-inositol monophosphatase, but unlike lithium does not enhance agonist-induced inositol phosphate accumulation". Biochemical Journal 291, nr 2 (15.04.1993): 369–74. http://dx.doi.org/10.1042/bj2910369.
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Despite limiting side-effects, lithium is the drug of choice for the treatment of bipolar depression. Its action may be due, in part, to its ability to dampen phosphatidylinositol turnover by inhibiting myo-inositol monophosphatase. Beryllium has been identified as a potent inhibitor of partially purified myo-inositol monophosphatase isolated from rat brain (Ki = 150 nM), bovine brain (Ki = 35 nM), and from the human neuroblastoma cell line SK-N-SH (Ki = 85 nM). It is over three orders of magnitude more potent than LiCl (Ki = 0.5-1.2 mM). Kinetic analysis reveals that beryllium is a competitive inhibitor of myo-inositol monophosphatase, in contrast with lithium which is an uncompetitive inhibitor. Inhibition of exogenous [3H]inositol phosphate hydrolysis by beryllium (IC50 = 250-300 nM) was observed to the same maximal extent as that seen with lithium in permeabilized SK-N-SH cells, reflecting inhibition of cellular myo-inositol monophosphatase. However, in contrast with that observed with lithium, agonist-induced accumulation of inositol phosphate was not observed with beryllium in permeabilized and non-permeabilized SK-N-SH cells and in rat brain slices. Similar results were obtained in permeabilized SK-N-SH cells when GTP-gamma-S was used as an alternative stimulator of inositol phosphate accumulation. The disparity in the actions of beryllium and lithium suggest that either (1) selective inhibition of myo-inositol monophosphatase does not completely explain the action of lithium on the phosphatidylinositol cycle, or (2) that uncompetitive inhibition of myo-inositol monophosphatase is a necessary requirement to observe functional lithium mimetic activity.
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Bailyes, E. M., M. A. J. Ferguson, C. A. Colaco i J. P. Luzio. "Inositol is a constituent of detergent-solubilized immunoaffinity-purified rat liver 5′-nucleotidase". Biochemical Journal 265, nr 3 (1.02.1990): 907–9. http://dx.doi.org/10.1042/bj2650907.
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myo-Inositol analysis of detergent-solubilized immunoaffinity-purified rat liver 5′-nucleotidase showed the presence of 1 mol of myo-inositol/mol of enzyme monomer. This provides unequivocal evidence that the ectoenzyme 5′-nucleotidase is attached to liver membranes by a glycosyl-phosphatidylinositol lipid anchor.
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SALAMONCZYK, G. M., i K. M. PIETRUSIEWICZ. "ChemInform Abstract: A Practical Three-Step Conversion of myo-Inositol into D-myo-Inositol 1-Phosphate." ChemInform 23, nr 19 (22.08.2010): no. http://dx.doi.org/10.1002/chin.199219300.
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Roseff, Scott, i Marta Montenegro. "Inositol Treatment for PCOS Should Be Science-Based and Not Arbitrary". International Journal of Endocrinology 2020 (27.03.2020): 1–8. http://dx.doi.org/10.1155/2020/6461254.
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The aim of this paper is to critically analyze the composition of many inositol-based products currently used to treat Polycystic Ovary Syndrome (PCOS). Several different combinations of myo-inositol and D-chiro-inositol, with and without additional compounds such as micro- and macroelements, vitamins, and alpha-lipoic acid, have been formulated over the years. Such therapeutic proposals do not take various features of inositol stereoisomers into consideration. As an example, it is important to know that D-chiro-inositol treatment may be beneficial when administered in low doses, yet the progressive increase of its dosage results in the loss of its advantageous effects on the reproductive performance of women and a deterioration in the quality of blastocysts created via in vitro fertilization (IVF). In addition, we have to consider that the intestinal absorption of myo-inositol is reduced by the simultaneous administration of D-chiro-inositol since the two stereoisomers compete with each other for the same transporter that has similar affinity for each of them. A decrease in myo-inositol absorption is also found when it is coadministered with inhibitors of sugar intestinal absorption and/or types of sugars such as sorbitol, maltodextrin, and sucralose. The combination of these may require higher amounts of myo-inositol in order to reach a therapeutic dosage compared to inositol administration alone, a particularly important fact when physicians strive to obtain a specific plasma level of the stereoisomer. Finally, we must point out that D-chiro-inositol was found to be an aromatase inhibitor which increases androgens and may have harmful consequences for women. Therefore, the inositol supplements used in PCOS treatment must be carefully defined. Clinical evidence has demonstrated that the 40 : 1 ratio between myo-inositol and D-chiro-inositol is the optimal combination to restore ovulation in PCOS women. Therefore, it is quite surprising to find that inositol-based treatments for PCOS seem to be randomly chosen and are often combined with useless or even counterproductive molecules, all of which can weaken myo-inositol’s efficacy. Such treatments clearly lack therapeutic rationale.