Wu L N, Fisher R R
J Biol Chem. 1982 Oct 10;257(19):11680-3.
Bovine heart submitochondrial particle energy-linked NADH leads to NADP+ transhydrogenase also catalyzes transhydrogenation between NADPH and NADP+. The stereochemistry of hydride ion transfer in the NADH leads to NADP+ reaction involves the nicotinamide 4A locus of NADH and the 4B locus of NADPH. In this paper it is demonstrated that during NADPH leads to NADP+ transhydrogenation the NADP+ is reduced exclusively at the 4B locus and that oxidation of NADPH is predominately at the 4B locus. Reduction of [4-3H]NADP+ by NADPH yielded [4A-3H]NADPH as the only product. Oxidation of [4A-3H]NADPH by NADP+ resulted in the conversion of nearly 33% of the label into [4-3H]NADP+, whereas the oxidation of [4B-3H] NADPH yielded only about a 6.5% conversion. These data suggest that while a small portion of total energy-linked NADPH leads to NADP+ transhydrogenation results from the binding of NADPH at the NAD domain of the active site with hydride transfer to NADP+ bound at the NADP domain, most of the reaction occurs by a mechanism in which both substrates are bound sequentially at the NADP domain. It is proposed that NADPH leads to NADP+ transhydrogenation represents a partial reaction of NADH leads to NADP+ transhydrogenation which involves the participation of a reduced-enzyme intermediate.
牛心亚线粒体颗粒中能量偶联的NADH生成NADP⁺转氢酶也催化NADPH和NADP⁺之间的转氢作用。NADH生成NADP⁺反应中氢负离子转移的立体化学涉及NADH的烟酰胺4A位点和NADPH的4B位点。本文证明，在NADPH生成NADP⁺转氢过程中，NADP⁺仅在4B位点被还原，且NADPH的氧化主要发生在4B位点。NADPH还原[4-³H]NADP⁺仅产生[4A-³H]NADPH这一种产物。[4A-³H]NADPH被NADP⁺氧化时，近33%的标记物转化为[4-³H]NADP⁺，而[4B-³H]NADPH的氧化仅产生约6.5%的转化率。这些数据表明，虽然能量偶联的NADPH生成NADP⁺转氢总量中的一小部分是由于NADPH在活性位点的NAD结构域结合并将氢化物转移至在NADP结构域结合的NADP⁺所致，但大多数反应是通过两种底物依次在NADP结构域结合的机制发生的。有人提出，NADPH生成NADP⁺转氢代表了NADH生成NADP⁺转氢的部分反应，其中涉及还原酶中间体的参与。
