Overall kinetic mechanism of 6-phosphogluconate dehydrogenase from Candida utilis

• Published in: Biochemistry (Easton) Vol. 32; no. 8; pp. 2036 - 2040
• Main Authors: Berdis, Anthony J, Cook, Paul F
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 02-03-1993
• Subjects: Analytical, structural and metabolic biochemistry; Biological and medical sciences; Candida - enzymology; Candida utilis; Enzymes and enzyme inhibitors; Fundamental and applied biological sciences. Psychology; Kinetics; Mathematics; Models, Theoretical; NADP - metabolism; Oxidation-Reduction; Oxidoreductases; Phosphogluconate Dehydrogenase - isolation & purification; Phosphogluconate Dehydrogenase - metabolism; Fungi; Candida utilis; Yeast; Product inhibition; Phosphogluconate dehydrogenase; Enzyme; Initial rate; Reaction mechanism; Fungi Imperfecti; Kinetics; Thallophyta
• ISSN: 0006-2960; 1520-4995
• DOI: 10.1021/bi00059a021

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.