Stereochemistry of NADPH leads to NADP+ transhydrogenation catalyzed by bovine heart mitochondrial pyridine dinucleotide transhydrogenase.
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.
D000818:Animals; D002417:Cattle; D008928:Mitochondria / Q000201:enzymology*; D008929:Mitochondria, Heart / Q000201:enzymology*; D009247:NADH, NADPH Oxidoreductases / Q000378:metabolism*; D009249:NADP / Q000378:metabolism*; D009250:NADP Transhydrogenases / Q000378:metabolism*; D010084:Oxidation-Reduction; D013237:Stereoisomerism; D013367:Submitochondrial Particles / Q000201:enzymology*
D009249:NADP; D009247:NADH, NADPH Oxidoreductases; D009250:NADP Transhydrogenases