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Glucose-6-Phosphate Dehydrogenase from the Chemolithotroph Thiobacillus ferrooxidans
Authors:Robert Tabita and  D G Lundgren
Abstract:Glucose-6-phosphate dehydrogenase was partially purified from both glucose-grown and iron-glucose-grown Thiobacillus ferrooxidans. The enzyme possesses a dual nucleotide specificity for either nicotinamide adenine dinucleotide phosphate (NADP) or nicotinamide adenine dinucleotide (NAD) and has a molecular weight of 110,000 as determined by gel electrophoresis. Evidence is presented that T. ferrooxidans glucose-6-phosphate dehydrogenase is identical when isolated from cells grown mixotrophically (iron-glucose grown) or cells grown heterotrophically (glucose-grown cells). The enzyme is activated by Mg(2+), and to a lesser extent by low concentrations of Mn(2+). Reduced NAD inhibits the enzyme from T. ferrooxidans. No deviation from normal Michaelis-Menten kinetics was observed in velocity versus substrate concentration experiments. Adenosine triphosphate exerted a profound inhibition of the enzyme; the effect was 10 times more pronounced in the presence of NAD as compared to NADP. The physiological significance of this inhibition is discussed.
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