Liochev S, Fridovich I
Arch Biochem Biophys. 1986 Oct;250(1):139-45. doi: 10.1016/0003-9861(86)90710-1.
Rat liver microsomes catalyze a vanadate-stimulated oxidation of NAD(P)H, which is augmented by paraquat and suppressed by superoxide dismutase, but not by catalase. NADPH oxidation was a linear function of the concentration of microsomes in the absence of vanadate, but was a saturating function in the presence of vanadate. Microsomes did not catalyze a vanadate-stimulated oxidation of reduced nicotinamide mononucleotide (NMNH), but gained this ability when NADPH was also present. When the concentration of NMNH was much greater than that of NADPH a minimal average chain length could be calculated from 1/2 the ratio of NMNH oxidized per NADPH added. The term chain length, as used here, signifies the number of molecules of NMNH oxidized per initiating event. Chain length could be increased by increasing [vanadate] and [NMNH] and by decreasing pH. Chain lengths in excess of 30 could easily be achieved. The Km for NADPH, arrived at from saturation of its ability to trigger NMNH oxidation by microsomes in the presence of vanadate, was 1.5 microM. Microsomes or the outer mitochondrial membrane was able to catalyze the vanadate-stimulated oxidation of NADH or NADPH but only the oxidation of NADPH was accelerated by paraquat. The inner mitochondrial membrane was able to cause the vanadate-stimulated oxidation of NAD(P)H and in this case paraquat stimulated the oxidation of both pyridine coenzymes. Our results indicate that vanadate stimulation of NAD(P)H oxidation by biomembranes is a consequence of vanadate stimulation of NAD(P)H or NMNH oxidation by O-2, rather than being due to the existence of vanadate-stimulated NAD(P)H oxidases or dehydrogenases.
大鼠肝脏微粒体可催化钒酸盐刺激的NAD(P)H氧化反应，百草枯可增强该反应，超氧化物歧化酶可抑制该反应，但过氧化氢酶无此作用。在无钒酸盐存在时，NADPH氧化是微粒体浓度的线性函数，但在有钒酸盐存在时是饱和函数。微粒体不能催化钒酸盐刺激的还原型烟酰胺单核苷酸（NMNH）氧化反应，但当同时存在NADPH时则获得此能力。当NMNH的浓度远高于NADPH时，可根据每添加一个NADPH所氧化的NMNH的比例的一半计算出最小平均链长。此处使用的链长一词表示每个起始事件氧化的NMNH分子数。链长可通过增加[钒酸盐]和[NMNH]以及降低pH来增加。链长超过30很容易实现。在有钒酸盐存在的情况下，通过微粒体触发NMNH氧化能力的饱和得出的NADPH的Km为1.5微摩尔。微粒体或线粒体外膜能够催化钒酸盐刺激的NADH或NADPH氧化反应，但只有NADPH的氧化反应能被百草枯加速。线粒体内膜能够引起钒酸盐刺激的NAD(P)H氧化反应，在这种情况下，百草枯可刺激两种吡啶辅酶的氧化反应。我们的结果表明，生物膜对NAD(P)H氧化反应的钒酸盐刺激是钒酸盐刺激O-2对NAD(P)H或NMNH氧化反应的结果，而不是由于存在钒酸盐刺激的NAD(P)H氧化酶或脱氢酶。
