Title

Overall Kinetic Mechanism of 6-Phosphogluconate Dehydrogenase From Candida Utilis

Document Type

Article

Publication Date

3-1-1993

Publication Title

Biochemistry

Abstract

A complete initial velocity study of the 6-phosphogluconate dehydrogenase from Candida utilis at pH 7 and 25 OC 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.

Comments

This work was supported by grants to P.F.C. from NIH (GM 36799) and the Robert A. Welch Foundation (B-1031).

DOI

10.1021/bi00059a021

Volume

32

Issue

8