Glucose-6-phosphate dehydrogenase regulation during hypometabolism

Glucose-6-phosphate dehydrogenase (G6PDH) from hepatopancreas of the land snail, Otala lactea, shows distinct changes in properties between active and estivating (dormant) states, providing the first evidence of pentose phosphate cycle regulation during hypometabolism. Compared with active snails, G6PDH Vmax increased by 50%, Km for glucose-6-phosphate decreased by 50%, Ka Mg x citrate decreased by 35%, and activation energy (from Arrhenius plots) decreased by 35% during estivation. DEAE-Sephadex chromatography separated two peaks of activity and in vitro incubations stimulating protein kinases or phosphatases showed that peak I (low phosphate) G6PDH was higher in active snails (57% of activity) whereas peak II (high phosphate) G6PDH dominated during estivation (71% of total). Kinetic properties of peaks I and II forms mirrored the enzyme from active and estivated states, respectively. Peak II G6PDH also showed reduced sensitivity to urea inhibition of activity and greater stability to thermolysin protease treatment. The interconversion of G6PDH between active and estivating forms was linked to protein kinase G and protein phosphatase 1. Estivation-induced phosphorylation of G6PDH may enhance relative carbon flow through the pentose phosphate cycle, compared with glycolysis, to help maintain NADPH production for use in antioxidant defense.     

Glucose-6-phosphate dehydrogenase and malate dehydrogenase enzyme electrophoretic patterns amongst strains of Bacteroides fragilis

Fifty-two strains of Bacteroides fragilis were examined for their enzyme electrophoretic patterns of glucose-6-phosphate dehydrogenase (G6PDH) and malate dehydrogenase (MDH). All strains tested possessed high levels of both enzymes but the G6PDH reduced NADP whereas MDH was NAD-dependent. Twenty-seven strains produced single bands of both G6PDH and MDH. In all cases G6PDH migrated faster than MDH. Strains clustered by a single linkage algorithm were recovered in eight clusters at the 77% similarity level. The remaining 25 strains produced multiple bands of one or both enzymes. These were recovered in six clusters at the 72% similarity level using the same algorithm. The results of this study revealed considerable heterogeneity of enzyme patterns within B. fragilis.     

Glucose-6-phosphate dehydrogenase Boston

Summary A hitherto undescribed variant of erythrocyte glucose-6-phosphate dehydrogenase (G-6-PD) activity, G-6-PD Boston, is described in a 24-year-old Caucasian male of Polish-Jewish ancestry. A marked decrease in red cell G-6-PD activity was associated, in this individual, with a compensated hemolytic process. The electrophoretic mobility of the partially purified enzyme on cellulose acetate at pH 9.1 and on starch gel was indistinguishable from normal but the apparent K_m for both G-6-PD (18–21 M) and NADP (1.7–2.2) was significantly decreased. Preliminary evidence supports the concept that G-6-PD Boston may not be extremely rare among this particular population group.     

Glucose-6-phosphate dehydrogenase in Thailand

Summary Erythrocyte G6PD from 1157 nondeficient Thai males was studied electrophoretically. The enzyme from four subjects showed abnormal mobility. Characterization of the enzyme revealed three new variants: G6PDs Ayutthaya (n=2), S-Sakorn, and Chao Phya.     

Glucose-6-phosphate dehydrogenase deficiency in Iraq

Summary Glucose-6-phosphate dehydrogenase was tested in the blood of 305 males and 394 females, with Beutler's fluorescent spot test being used for screening. The percentage of deficiency was estimated at 12.4% for males and 8.8% for females of all ages; it was, however, highest among children and lowest among those over 50 years.The efficiency of the fluorescent screening test in detecting heterozygote females was estimated at 35% and was derived by determining gene frequencies and comparing the expected and the observed.     

Glucose-6-phosphate dehydrogenase from rabbit erythrocytes

Glucose-6-phosphate dehydrogenase (d-glucose-6-phosphate:NADP⁺ 1-oxidoreductase, EC 1.1.1.49) was purified from rabbit erythrocytes. Initial velocity studies and product and dead-end inhibitor studies with this enzyme are consistent with a rapid equilibrium random mechanism with an enzyme-NADPH-glucose 6-phosphate dead-end complex.     

Glucose-6-phosphate dehydrogenase deficiency in Spain

Examination of 2520 male subjects in Spain by the Dye Reduction Test revealed five cases of Glucose-6-phosphate dehydrogenase deficiency, all originating from the east coast of Spain and the Balearic Islands. In these areas the enzyme deficiency seems to occur focally at low frequencies near 1%.Qui de fetge va que no passi pel favar! Who suffers from the liver should not pass through a fava field!(Direktor: Prof. Dr. H. Hungerland)     

Glucose-6-phosphate dehydrogenase of Anabaena sp.

The kinetic and molecular properties of cyanobacterial glucose-6-phosphate dehydrogenase, partly purified from Anabaena sp. ATCC 27893, show that it undergoes relatively slow, reversible transitions between different aggregation states which differ in catalytic activity. Sucrose gradient centrifugation and polyacrylamide gel electrophoresis reveal three principal forms, with approximate molecular weights of 120 000 (M ₁), 240 000 (M ₂) and 345 000 (M ₃). The relative catalytic activities are: M ₁M ₂<M ₃. In concentrated solutions of the enzyme, the equilibrium favors the more active, oligomeric forms. Dilution in the absence of effectors shifts the equilibrium in favor of the M ₁ form, with a marked diminution of catalytic activity. This transition is prevented by a substrate, glucose-6-phosphate, and also by glutamine. The other substrate, nicotinamide adenine dinucleotide phosphate (NADP⁺), and (in crude cell-free extracts) ribulose-1,5-diphosphate are negative effectors, which tend to maintain the enzyme in the M ₁ form. The equilibrium state between different forms of the enzyme is also strongly dependent on hydrogen ion concentration. Although the optimal pH for catalytic activity is 7.4, dissociation to the hypoactive M ₁ form is favored at pH values above 7; a pH of 6.5 is optimal for maintenace of the enzyme in the active state. Reduced nicotamide adenine dinucleotide phosphate (NADPH) and adenosine 5-triphosphate (ATP), inhibit catalytic activity, but do not significantly affect the equilibrium state. The relevance of these findings to the regulation of enzyme activity in vivo is discussed.Abbreviations G6PD glucose-6-phosphate dehydrogenase - 6PGD 6-phosphogluconate dehydrogenase - RUDP ribulose-1,5-diphosphate - G6P glucose-6-phosphate - 6PG 6-phosphogluconate     

Glucose-6-phosphate dehydrogenase and 6-phosphogluconic acid dehydrogenase of wild oat seeds

The presence of the initial enzymes of the pentose phosphate pathway, namely glucose-6-phosphate dehydrogenase and 6-phosphogluconic acid dehydrogenase, has been demonstrated in dormant seed of wild oat. Before a partial characterization of these enzymes was made, an inherent NADP-reducing activity and an enzyme deactivating component, both present in the crude extract, were removed by ammonium sulphate precipitation and subsequent desalting. Both enzymes were then shown to be NADP-specific. Typical Michaelis-Menten kinetics were shown by each enzyme towards NADP and their respective substrates. Soluble cytoplasmic dehydrogenase enzymes were present in both embryo and endosperm extracts.     

Glucose-6-phosphate dehydrogenase variants in Hawaii.

Sequence analysis has been performed on the DNA of 13 glucose-6-phosphate dehydrogenase (G6PD) deficient males from Hawaii, 6 of Filipino, 6 of Laotian, and 1 of Chinese extraction. Four different mutations were found: A-->T at cDNA nt 835, G-->A at nt 871, C-->T at nt 1360, and G-->A at nt 1388. The mutations at nt 835 and nt 1360 have not been described previously, and the latter, in particular, appears to be relatively common. The nt 1360 mutation changes the same codon as is altered in a previously described mutation, G6PD Andalus.