title: Partial purification and some kinetic properties of glucose-6-phosphate dehydrogenase from Phycomyces blakesleeanus.
abstract: Glucose-6-phosphate dehydrogenase from sporangiophores of Phycomyces blakesleeanus NRRL 1555 (-) was partially purified. The enzyme showed a molecular weight of 85 700 as determined by gel-filtration. NADP+ protected the enzyme from inactivation. Magnesium ions did not affect the enzyme activity. Glucose-6-phosphate dehydrogenase was specific for NADP+ as coenzyme. The reaction rates were hyperbolic functions of substrate and coenzyme concentrations. The Km values for NADP+ and glucose 6-phosphate were 39.8 and 154.4 microM, respectively. The kinetic patterns, with respect to coenzyme and substrate, indicated a sequential mechanism. NADPH was a competitive inhibitor with respect to NADP+ (Ki = 45.5 microM) and a non-competitive inhibitor with respect to glucose 6-phosphate. ATP inhibited the activity of glucose-6-phosphate dehydrogenase. The inhibition was of the linear-mixed type with respect to NADP+, the dissociation constant of the enzyme-ATP complex being 2.6 mM, and the enzyme-NADP+-ATP dissociation constant 12.8 mM.
mesh_terms: D000255:Adenosine Triphosphate / Q000494:pharmacology; D005954:Glucosephosphate Dehydrogenase / Q000302:isolation & purification* / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008970:Molecular Weight; D009090:Mucorales / Q000201:enzymology*; D010800:Phycomyces / Q000201:enzymology*; D013379:Substrate Specificity
chemical_list: D000255:Adenosine Triphosphate; D005954:Glucosephosphate Dehydrogenase