Iannone A, Tomasi A, Vannini V, Swartz H M
University of Illinois College of Medicine, Urbana.
Biochim Biophys Acta. 1990 Jun 20;1034(3):285-9. doi: 10.1016/0304-4165(90)90052-x.
As part of an ongoing study of the role of subcellular fractions on the metabolism of nitroxides, we studied the metabolism of a set of seven nitroxides in microsomes obtained from rat liver. The nitroxides were chosen to provide information on the effects of the type of charge, lipophilicity and the ring on which the nitroxide group is located. Important variables that were studied included adding NADH, adding NADPH, induction of enzymes by intake of phenobarbital and the effects of oxygen. Reduction to nonparamagnetic derivatives and oxidation back to paramagnetic derivatives were measured by electron-spin resonance spectroscopy. In general, the relative rates of reduction of nitroxides were similar to those observed with intact cells, but the effects of the various variables that were studied often differed from those observed in intact cells. The rates of reduction were very slow in the absence of added NADH or NADPH. The relative effect of these two nucleotides changed when animals were fed phenobarbital, and paralleled the levels of NADPH cytochrome c reductase, cytochrome P-450, cytochrome b5 and NADH cytochrome c reductase; results with purified NADPH-cytochrome c reductase were consistent with these results. In microsomes from uninduced animals the rate of reduction was about 10-fold higher in the absence of oxygen. The products of reduction of nitroxides by microsomes were the corresponding hydroxylamines. We conclude that there are significant NADH- and NADPH-dependent paths for reduction of nitroxides by hepatic microsomes, probably involving cytochrome c reductases and not directly involving cytochrome P-450. From this, and from parallel studies now in progress in our laboratory, it seems likely that metabolism by microsomes is an important site of reduction of nitroxides. However, mitochondrial metabolism seems to play an even more important role in intact cells.
作为一项关于亚细胞组分在氮氧化物代谢中作用的正在进行的研究的一部分，我们研究了从大鼠肝脏获得的微粒体中一组七种氮氧化物的代谢。选择这些氮氧化物是为了提供有关电荷类型、亲脂性以及氮氧化物基团所在环的影响的信息。所研究的重要变量包括添加NADH、添加NADPH、通过摄入苯巴比妥诱导酶以及氧气的影响。通过电子自旋共振光谱法测量还原为非顺磁性衍生物和氧化回顺磁性衍生物的情况。一般来说，氮氧化物的相对还原速率与在完整细胞中观察到的相似，但所研究的各种变量的影响往往与在完整细胞中观察到的不同。在没有添加NADH或NADPH的情况下，还原速率非常缓慢。当给动物喂食苯巴比妥时，这两种核苷酸的相对作用发生了变化，并且与NADPH细胞色素c还原酶、细胞色素P-450、细胞色素b5和NADH细胞色素c还原酶的水平平行；纯化的NADPH-细胞色素c还原酶的结果与这些结果一致。在未诱导动物的微粒体中，在无氧条件下还原速率大约高10倍。微粒体还原氮氧化物的产物是相应的羟胺。我们得出结论，肝脏微粒体存在显著的依赖NADH和NADPH的氮氧化物还原途径，可能涉及细胞色素c还原酶，而不直接涉及细胞色素P-450。据此以及我们实验室正在进行的平行研究，微粒体代谢似乎很可能是氮氧化物还原的一个重要部位。然而，线粒体代谢在完整细胞中似乎起着更重要的作用。
