Differentiation of glucose-6-phosphate dehydrogenase isozymes and morphogenesis in blastocladiella emersonii

Summary Studies were made of some of the properties of a NADP-specific Glucose-6-phosphate dehydrogenase present in the OC and RS cells of the aquatic fungus, Blastocladiella emersonii, the former harvested at their generation time and the latter at their morphological point of no return. A more detailed analysis was then made of the distribution of soluble and bound forms of the dehydrogenase during the exponential growth and subsequent differentiation of the RS cell, as well as the changes which occurred in the isozymes of this enzyme during the same developmental period. The results, together with some related, previously published work, were discussed with emphasis on the relation between biochemical and morphological differentiation in B. emersonii.     

The structural subunit of glucose-6-phosphate dehydrogenase (baker's yeast).

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.     

Characterization of an inhibitor of glucose-6-phosphate dehydrogenase

A strong inhibitor of G6PDH has been detected in rat liver homogenates. The inhibitor, isolated by ultrafiltration methods, proved to be very stable under incubation with trypsin and high temperatures. Gel-filtration through Sephadex G-75 showed it to have a molecular weight of 3,500 daltons, though perchloric acid treatment produced a light form of 900 daltons. Both forms of inhibitor act as competitive inhibitor with respect to G6P and exhibit non-competitive inhibition pattern with respect to NADP+. Physical and kinetic properties, and the increase of G6PDH activity at low NADP+ concentrations, in the presence of NADPH and inhibitor or palmitoyl-CoA, in relation to the G6PDH activity in presence of NADPH, lead to the identification of the low-molecular weight inhibitor as palmitoyl-CoA.     

The molecular basis of glucose-6-phosphate dehydrogenase deficiency.

With more than 300 different variants reported, the human enzyme glucose-6-phosphate dehydrogenase (G6PD; EC 1.1.1.49) is one of the most polymorphic proteins known. An estimated 400 million people throughout the world are deficient in G6PD; numerous lines of evidence indicate that this is because female heterozygotes have a selective advantage in malaria infections. The cloning of the G6PD gene has made it possible to clarify the molecular basis underlying this enzyme deficiency and polymorphism.     

Drug-induced haemolysis in glucose-6-phosphate dehydrogenase deficiency.

People with the variants of glucose-6-phosphate dehydrogenase (GPD) deficiency common in the southern Chinese (Canton, B(-)Chinese, and Hong Kong-Pokfulam) have a moderate shortening of red-cell survival but no anaemia when they are in the steady state. With a cross-transfusion technique, primaquine, nitrofurantoin, and large doses of aspirin were found to aggravate the haemolysis while sulphamethoxazole did so only in some people. Individual differences in drug metabolism may be the reason for this. Many commonly used drugs reported to accentuate haemolysis in GPD deficiency did not shorten red-cell survival.     

Development of a glucose-6-phosphate biosensor based on coimmobilized p-hydroxybenzoate hydroxylase and glucose-6-phosphate dehydrogenase

This work reports the development of an amperometric glucose-6-phosphate biosensor by coimmobilizing p-hydroxybenzoate hydroxylase (HBH) and glucose-6-phosphate dehydrogenase (G6PDH) on a screen-printed electrode. The principle of the determination scheme is as follows: G6PDH catalyzes the specific dehydrogenation of glucose-6-phosphate by consuming NADP(+). The product, NADPH, initiates the irreversible the hydroxylation of p-hydroxybenzoate by HBH in the presence of oxygen to produce 3,4-dihydroxybenzoate, which results in a detectable signal due to its oxidation at the working electrode. The sensor shows a broad linear detection range between 2 microM and 1000 microM with a low detection limit of 1.2 microM. Also, it has a fast measuring time which can achieve 95% of the maximum current response in 20s after the addition of a given concentration of glucose-6-phosphate with a short recovery time (2 min).     

Cortisol levels in glucose-6-phosphate dehydrogenase deficiency.

The aim of the present study was to investigate cortisol levels under basal conditions and in response to ACTH stimulation in male patients with glucose-6-phosphate dehydrogenase (G-6-PD) deficiency. The study included 14 male controls and 12 patients with G-6-PD deficiency matched for age and race. Fasting blood samples were taken from all the subjects at rest, and 30, 60 and 120 min after the infusion of 0.25 mg of corticotropin for cortisol determination. The mean cortisol levels observed in the first hour after ACTH stimulation in the G-6-PD-deficient patients were significantly (p = 0.03) lower than in the control group. No significant differences were observed between patients and controls at rest, and in the second hour after stimulation. These data suggest that, in the adrenals, G-6-PD plays a role in the initial phase of cortisol production. However, 1 h after ACTH stimulation, G-6-PD probably is no longer rate limiting in the production of cortisol.     

Specific activities of 6-phosphogluconate dehydrogenase,glucose-6-phosphate dehydrogenase and glucose-6-phosphate isomerase during Bufo bufo development

It has been suggested by some authors that during amphibian development, due to the higher glucose-6-phosphate dehydrogenase (EC 1.1.1.49) activity compared to that of 6-phosphogluconate dehydrogenase (EC 1.1.1.43), 6-phosphogluconate could accumulate in the embryo tissues and regulate the channelling of glucose-6-phosphate into glycolysis. Here, on the base of the specific activities of glucose-6-phosphate dehydrogenase, 6-phosphogluconate dehydrogenase and glucose-6-phosphate isomerase (EC 5.3.1.9) found in the embryos of Bufo bufo during development, it is discussed whether 6-phosphogluconate can accumulate and play a regulative role on glucose-6-phosphate metabolism in the anuran embryo.     

A kinetic study of glucose-6-phosphate dehydrogenase.

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.     

Hyperanodic forms of human glucose-6-phosphate dehydrogenase.

Pure glucose-6-phosphate dehydrogenase (D-glucose-6-phosphate:NADP+ 1-oxidoreductase, EC 1.1.1.49) is transformed into 'hyperanodic forms' when incubated at acidic pH and in the presence of NADP+ with excess of glucose-6-phosphate or with some 'NADP+ modifying proteins' purified from the same cells. The enzyme hyperanodic forms exhibit low isoelectric point, altered kinetic properties and high lability to heat, urea, and proteolysis. Differences between hyperanodic and native forms of glucose-6-phosphate dehydrogenase are also noted by microcomplement fixation analysis, ultraviolet absorbance difference spectrum and fluorescence emission spectrum. Drastic denaturation of the enzyme by urea and acid treatment did not suppress the difference of isoelectric point between native and hyperanodic forms of glucose-6-phosphate dehydrogenase. From our data we suggest that the conversion into hyperanodic forms could be due to the covalent binding on the enzyme of a degradation product of the pyridine nucleotide coenzyme. This modification could constitute a physiological transient step toward the definitive degradation of the enzyme.