Johnson M S, Kuby S A
Arch Biochem Biophys. 1986 Feb 15;245(1):271-81. doi: 10.1016/0003-9861(86)90214-6.
A study of the steady-state kinetics of NADH(NADPH)-cytochrome c reductase (FMN-containing) from ale yeast (M. S. Johnson and S. A. Kuby (1985) J. Biol. Chem. 260, 12341-12350) has led to a postulated three-substrate random-ordered hybrid mechanism, where NAD(P)H and FMN add randomly and very likely in a steady-state fashion, followed by an ordered addition of cytochrome c. Kinetic parameters have been derived from this mechanism. Arrhenius plots showed large differences between NADH and NADPH, as the substrate-reductant. Menadione accelerated cytochrome c reduction and also O2 uptake, but vitamin K1 and coenzyme Q10 were ineffective as electron mediators, possibly as a result of their insolubility. With NADPH as the substrate-reductant, the order of the rate of reduction of electron acceptors was ferricyanide greater than DCIP greater than cytochrome c greater than oxygen; with menadione, the specificity sequence was cytochrome c greater than ferricyanide greater than DCIP greater than oxygen. With NADH, the order was ferricyanide greater than cytochrome c greater than oxygen greater than DCIP, which changed to cytochrome c greater than ferricyanide greater than oxygen greater than DCIP on addition of menadione. Cytochrome b5 was also reduced in the absence of oxygen. No transhydrogenase activity was observed, but the reduced thionicotinamide analogs of NADH and NADPH acted as substrates. Superoxide dismutase inhibited cytochrome c reduction in air by 50%, but O2-. was not necessary for cytochrome c reduction, as evidenced by the increase in rate in the absence of O2. The product of the reaction with oxygen appeared to be H2O2.
一项关于啤酒酵母中含黄素单核苷酸的NADH（NADPH）-细胞色素c还原酶稳态动力学的研究（M. S. 约翰逊和S. A. 库比（1985年），《生物化学杂志》260卷，第12341 - 12350页）得出了一种假定的三底物随机有序混合机制，其中NAD(P)H和黄素单核苷酸随机且很可能以稳态方式添加，随后细胞色素c按顺序添加。动力学参数已从该机制推导得出。阿累尼乌斯曲线显示，作为底物还原剂的NADH和NADPH之间存在很大差异。甲萘醌加速了细胞色素c的还原以及氧气的摄取，但维生素K1和辅酶Q10作为电子介质无效，可能是由于它们不溶。以NADPH作为底物还原剂时，电子受体还原速率的顺序为铁氰化物大于2,6 - 二氯靛酚大于细胞色素c大于氧气；以甲萘醌为介质时，特异性顺序为细胞色素c大于铁氰化物大于2,6 - 二氯靛酚大于氧气。以NADH为底物时，顺序为铁氰化物大于细胞色素c大于氧气大于2,6 - 二氯靛酚，添加甲萘醌后变为细胞色素c大于铁氰化物大于氧气大于2,6 - 二氯靛酚。在无氧条件下细胞色素b5也会被还原。未观察到转氢酶活性，但NADH和NADPH的还原硫代烟酰胺类似物可作为底物。超氧化物歧化酶在空气中抑制细胞色素c还原50%，但细胞色素c还原并不需要超氧阴离子，无氧时还原速率增加就证明了这一点。与氧气反应的产物似乎是过氧化氢。
