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Query: EC:1.1.1.49 (glucose-6-phosphate dehydrogenase)
 7,794 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The steady state kinetics of pig liver glucose-6-phosphate dehydrogenase is consistent with an ordered, sequential mechanism in which NADP is bound first and NADPH released last. Kia is 9.0 muM, Ka is 4.8 muM, and Kb is 36 muM. Glucosamine 6-phosphate, a substrate analogue and competitive inhibitor, is used to help rule out a possible random mechanism. ADP is seen to form a complex with the free form of the enzyme whereas ATP forms a complex with both the free and E-NADP forms of the enzyme. The KI for the E-ADP complex is 1.9 mM, while the Ki values for the E-ATP and E-NADP-ATP complexes are 7.2 and 4.5 mM, respectively.
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PMID:A kinetic study of glucose-6-phosphate dehydrogenase. 0 40

The effects of lowering the liver pyridoxal phosphate (PLP) concentration by vitamin B-6 deficiency on the stability of several rat liver enzymes were examined. Three PLP-dependent enzymes (serine dehydratase, ornithine-delta-aminotransferase, and tyrosine aminotransferase) and two non-PLP-dependent enzymes (glucose-6-phosphate dehydrogenase and phosphoenolpyruvate carboxykinase) were induced in vitamin B-6 deficient and control rats by feeding them high-protein diets or by injecting them with glucagon or dexamethasone. The decline of each activity was followed after withdrawal of the inducer. Serine dehydratase activity declined more rapidly in vitamin B-6 deficient than in control liver; however, ornithine aminotransferase and tyrosine aminotransferase activities were equally stable in deficient and control liver. Ornithine aminotransferase was predominantly in holoenzyme form in both control and deficient rats, whereas tyrosine aminotransferase was predominantly in apoenzyme form in both groups. The proportion of serine dehydratase in apoenzyme was less stable than the holoenzyme. Activity changes of glucose-6-phosphate dehydrogenase and phosphoenolpyruvate carboxykinase in control and vitamin B-6 deficient rats were similar. The results suggest that differences in the stability of PLP-dependent enzymes in vitamin B-6 deficient rats depend upon differences in the proportions of these enzymes existing as holo- and apoenzyme.
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PMID:Stability of some pyridoxal phosphate-dependent enzymes in vitamin B-6 deficient rats. 0 99

The subunit molecular weight of glucose-6-phosphate dehydrogenase (G6PD) from baker's yeast has been evaluated. The subunit molecular weight value is shown to be 25,500 daltons by analytical ultracentrifugation, SDS-polyacrylamide gel electrophoresis, and the number of peptides produced by CNBr cleavage. The number of NADP binding sites was determined to be one per 25,500 dalton unit.
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PMID:The structural subunit of glucose-6-phosphate dehydrogenase (baker's yeast). 0 47

Feeding sheep a concentrate diet compared with grass diets increased the hepatic specific activities of the three glycolytic enzymes studied, and that of glucose-6-phosphate dehydrogenase (EC 1.1.1.49) and reduced the specific activity of D-fructose-I, 6-diphosphate I-phosphohydrolase (EC 3.1.3.11). The specific activities of phosphogluconate dehydrogenase (EC 1.1.1.43) and malate dehydrogenase (decarboxylating) (NADP) (EC 1.1.1.40) were unaffected by diet.
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PMID:The effects of grass and concentrate diets on the specific activities of some enzymes of hepatic carbohydrate metabolism in sheep. 0 5

A systematic study has been made of the pH- and temperature-dependency of the steady-state kinetic parameters of the stabilized two-subunit enzyme species of glucose-6-phosphate dehydrogenase, in the absence of superimposed association-dissociation reactions. The Vmax(app) data obtained in several buffers between pH 5 and 10 and at 18-32 degrees C lead to the postulate that at least two sets of protonic equilibria may govern the catalysis (one near pH 5.7 AT 25 DEGREES C and another near pH 9.2); furthermore, two pathways for product formation (i.e., two Vmax's) appear to be required to explain the biphasic nature of the log Vmax(app) vs. pH curves, with Vmax(basic) greater than Vmax(acidic + neutral). Of the several buffers explored, either a uniform degree of interaction or a minimal degree of buffer species interaction could be assessed from the enthalpy changes associated with the derived values for ionization constants attributed to the protonic equilibria in the enzyme-substrates ternary complexes for the case of Tris-acetate-EDTA buffers, at constant ionic strength. With the selection of this buffer at 0.1 (T/2) and at 25 and 32 degrees C, a self-consistent kinetic mechanism has emerged which allows for the random binding of the two fully ionized substrates to the enzyme via two major pathways, and product formation by both E-A--B- and HE-A--B-. As before (Kuby et al. Arch. Biochem, Biophys. 165, 153-178, 1974), a quasi-equilibrium is presumed, with rate-limiting steps (k + 5 and k + 5') at the interconversion of the ternary complexes. Values for the two sets of protonic equilibria defined by this mechanism (viz., pKk, pKH2 for the first ionizations, and pKk', pKH' for the second) could then be estimated. From their numerical values (e.g., at 25 degrees C: pKK = 5.7 PKH2 = 5.2; and pKK' = 9.1, PKH' = 8.2) and from the values for delta H degrees ioniz (e.g., delta H degrees pKK APPROXIMATELY 5.1 KCAL/MOL; DELTA H degrees pKK' APPROXIMATELY 11 KCAL/MOL), A POSTULATE IS PRESENTED WHICH ATTRIBUTES THESE Acid dissociation constants to an imidazole and epsilon-amino group, respectively.
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PMID:Glucose-6-phosphate dehydrogenase from brewers' yeast. The effects of pH and temperature on the steady-state kinetic parameters of the two-chain protein species. 0 21

9 variants of human erythrocyte glucose-6-phosphate dehydrogenase (G6PD) were isolated from erythrocytes of patients with G6PD deficiency and partially purified according to WHO program for stanartization of methods for studying G6PD. The results of physico-chemical study of these enzymes (determination of electrophoretic mobility, kappaM for G6P and NADP, pH optimum and thermostability) permit tu consider 5 of them to be new mutations of G6PD previously not described in literature. The observed high geterogeneity of variants of G6PD in Azerbaijan is discussed.
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PMID:[Description of new mutant forms of erythrocyte glucose-6-phosphate dehydrogenase in man]. 0 39

The values of Vmax and Km for the three genetic variants A, B, and A- of erythrocyte glucose-6-phosphate dehydrogenase have been determined at 10 different pH values in the range from 5.5 to 9.5, and at four different temperatures in the range from 18.5-40.0 degrees. The log Vmax versus pH curve for each of the enzymes shows a monotonic increase between pH 5.5 and 7, and a plateau from pH 7.5 upwards. These curves, and their temperature dependence, are compatible with the presence of a single ionizable group which, in its conjugate acid form, renders the enzyme-substrate complex inactive. The pK of this group is 6.94 at 18.5 degrees, and its enthalpy of ionization is 7.0 kcal mol-1. The log Km versus pH curves show a broad plateau between pH 6.2 and 8.2, interrupted by a sharp minimum at pH 7.2 for variant B, while variants A and A- show sharp maxima at pH 7.2 and 7.45, respectively. It is proposed that this unusual behavior depends on the dissociation of the tetrameric enzyme to dimers in this pH region. Specifically, it is shown that a sharp maximum or minimum of Km can arise if cooperative uptake or release of protons is linked to dimer formation, and if the degree of cooperativity is different for the free enzyme compared to the enzyme-substrate complex. The pH dependence of the equilibrium between the tetrameric and the dimeric form of the enzyme has been determined by gel filtration for the same three genetic variants B, A, and A-. In agreement with previous ultracentrifugal data, the enzyme is a tetramer in acid solution and a dimer in alkaline solution. The pH at which half of the enzyme is in dimeric form, under our experimental conditions, is 7.15 +/- 0.05 for variants A and B, and 7.35 +/- 0.05 for variant A-. These pH values correspond closely, for all three variants, to the sharp extrema in the pH dependence of their Km values for glucose 6-phosphate. From the measured dissociation equilibria, it can be inferred that the tetramer-dimer transition entails cooperative release of protons. The degree of cooperativity estimated from these data agrees closely with the independent estimate based on the pH dependence of Km.
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PMID:Genetic variants of human erythrocyte glucose-6-phosphate dehydrogenase. Kinetic and thermodynamic parameters of variants A, B, and A- in relation to quaternary structure. 0 48

The analogue of fructose 1,6-bisphosphate in which the phosphate group, -O-PO3H2, on C-6 is replaced by the phosphonomethyl group, -CH2-PO3H2, was made enzymically from the corresponding analogue of 3-phosphoglycerate. It was a substrate for aldolase, which was used to form it, but not for fructose 1,6-bisphosphatase. It was hydrolysed chemically to yield the corresponding analogue of fructose 6-phosphate [i.e. 6-deoxy-6-(phosphonomethyl)-D-fructose, or, more strictly, 6,7-dideoxy-7-phosphono-D-arabino-2-heptulose]. This proved to be a substrate for the sequential actions of glucose 6-phosphate isomerase, glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase. Thus seven out of the nine enzymes of the glycolytic and pentose phosphate pathways so far tested catalyse the reactions of the phosphonomethyl isosteres of their substrates.
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PMID:Phosphonomethyl analogues of hexose phosphates. 0 47

A mild oxidative stimulation of the hexose monophosphate pathway of human glucose-6-phosphate dehydrogenase (EC 1.1.1.49)-deficient erythrocytes (Mediterranean variant) causes a significant drop in NADPH. These results, other than to confirm that glucose-6-phosphate dehydrogenase deficiency is a product deficiency disorder, demonstrate that under oxidative stimulation glutathione reductase may become functionally impaired and GSSG cannot be reduced at a sufficient rate.
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PMID:NADP+ and NADPH in glucose-6-phosphate dehydrogenase-deficient erythrocytes under oxidative stimulation. 0 94

The development of obesity, hyperinsulinemia and six hepatic lipogenic enzymes in Avy/a mice were compared to that in a/a mice. Correlation between body weight, liver weight, plasma insulin concentration and activities of hepatic enzymes was analyzed. In the Avy/a mice, body weight, liver weight and plasma insulin level increased steadily as the mice aged. In the a/a mice, the change of these three parameters was much slower. Plasma insulin concentration in a/a mice did not increase until eight months of age. Compared with a/a mice, Avy/a mice had higher 6-phosphogluconate dehydrogenase and fatty acid synthetase activities at two months of age; lower citrate cleavage enzyme, glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase activities at three months of age; lower citrate cleavage enzyme and glucose-6-phosphate dehydrogenase and higher acetyl CoA carboxylase activities at five months of age; and higher malic enzyme, citrate cleavage enzyme and 6-phosphogluconate dehydrogenase activities at eight months of age. There were significant correlations between plasma insulin level and body weight and between plasma insulin level and the activities of malic enzyme and citrate cleavage enzyme in Avy/a mice. The correlation between body weight and malic enzyme and citrate cleavage enzyme activities disappeared after the analysis was adjusted for plasma insulin level.
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PMID:An analysis of the relationships among obesity, plasma insulin and hepatic lipogenic enzymes in "viable yellow obese" mice (Avy/a). 0 20


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