Berdis A J, Cook P F
Department of Biochemistry, Texas College of Osteopathic Medicine, Fort Worth 76107.
Biochemistry. 1993 Mar 2;32(8):2036-40. 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.
对产朊假丝酵母的6-磷酸葡萄糖酸脱氢酶在pH 7和25摄氏度下两个反应方向进行的完整初始速度研究表明，其具有快速平衡随机动力学机制，存在E:NADP:(5-磷酸核酮糖)和E:NADPH:(6-磷酸葡萄糖酸)终产物复合物。无论其他底物浓度如何，类似的底物-产物（NADP/NADPH和6-磷酸葡萄糖酸/5-磷酸核酮糖）对都是竞争性的，但对其他底物是非竞争性的，例如，NADPH对6-磷酸葡萄糖酸表现出非竞争性抑制。这种趋势对所有终产物类似物也成立，例如，ATP-核糖对NADP是竞争性的，对6-磷酸葡萄糖酸是非竞争性的。动力学抑制常数的定量分析支持了动力学机制的归属。氧化脱羧和还原羧化方向的最大速度之比为75。
