Overall kinetic mechanism of 6-phosphogluconate dehydrogenase from Candida utilis.
A complete initial velocity study of the 6-phosphogluconate dehydrogenase from Candida utilis at pH 7 and 25 degrees C in both reaction directions suggests a rapid equilibrium random kinetic mechanism with dead-end E:NADP:(ribulose 5-phosphate) and E:NADPH:(6-phosphogluconate) complexes. Like substrate-product (NADP/NADPH and 6-phosphogluconate/ribulose 5-phosphate) pairs are competitive whatever the concentration of the other substrates but noncompetitive versus the other substrates, e.g., NADPH exhibits noncompetitive inhibition versus 6-phosphogluconate. This trend also holds true for all dead-end analogs, e.g., ATP-ribose is competitive versus NADP and noncompetitive versus 6-phosphogluconate. A quantitative analysis of the kinetic inhibition constants supports the assignment of kinetic mechanism. The ratio of the maximum velocities in the oxidative decarboxylation and reductive carboxylation directions is 75.
Berdis
A J
AJ
Department of Biochemistry, Texas College of Osteopathic Medicine, Fort Worth 76107.
Cook
P F
PF
D002175:Candida / Q000201:enzymology*; D007700:Kinetics; D008433:Mathematics; D008962:Models, Theoretical; D009249:NADP / Q000378:metabolism; D010084:Oxidation-Reduction; D010734:Phosphogluconate Dehydrogenase / Q000302:isolation & purification / Q000378:metabolism*
D009249:NADP; D010734:Phosphogluconate Dehydrogenase