Rossi S C, Wetterhahn K E
Department of Chemistry, Dartmouth College, Hanover, New Hampshire 03755.
Carcinogenesis. 1989 May;10(5):913-20. doi: 10.1093/carcin/10.5.913.
Incubation of chromate with isolated rat liver submitochondrial particles under anaerobic conditions in vitro results in reduction of chromium(VI) and formation of chromium(V). In the presence of NADH, submitochondrial particles (SMPs) were active in reducing chromate as shown by UV-vis spectroscopic studies, and forming a chromium(V) species which was detectable by electron paramagnetic resonance spectroscopy. In the presence of succinate, SMPs were less effective in reducing chromate and forming chromium(V) relative to their NADH-dependent activity. However, SMPs showed a higher rate of oxygen depletion with NADH as compared to succinate as substrate, suggesting that differences in the NADH-dependent versus succinate-dependent chromate-reductase activity of SMPs is probably due to differences in efficiency of electron donation by succinate and NADH. The use of specific electron transport chain inhibitors allowed the sites of chromium(VI) reduction and chromium(V) formation in SMPs to be determined. Rotenone, antimycin and cyanide all produced approximately 40% inhibition of the NADH-dependent chromate-reductase activity. Thus, complex I (NADH:ubiquinone oxidoreductase) appears to be responsible for the inhibitor-insensitive, and complex IV (ferrocytochrome c:oxygen oxidoreductase) for the inhibitor-sensitive NADH-dependent chromium(VI) reduction and chromium(V) formation. Cyanide and antimycin produced approximately 50% inhibition of the succinate-dependent chromate-reductase activity of SMPs, while no detectable inhibition was observed with rotenone. These results confirm the chromate-reductase activity of complex IV, and suggest that complex II (succinate:ubiquinone oxidoreductase) is responsible for the inhibitor-insensitive succinate-dependent chromate-reductase activity of SMPs. Since chromium(VI) is effectively metabolized by electron transport chain complexes of the mitochondrial inner membrane in vitro, and chromium(V) is formed as an intermediate in the process, mitochondria may play a role in chromium(VI) carcinogenesis.
在体外厌氧条件下，将铬酸盐与分离的大鼠肝脏亚线粒体颗粒一起温育，会导致六价铬还原并形成五价铬。紫外可见光谱研究表明，在烟酰胺腺嘌呤二核苷酸（NADH）存在的情况下，亚线粒体颗粒（SMPs）具有还原铬酸盐的活性，并形成一种可通过电子顺磁共振光谱检测到的五价铬物种。相对于其依赖NADH的活性，在琥珀酸存在的情况下，SMPs还原铬酸盐和形成五价铬的效果较差。然而，与以琥珀酸为底物相比，以NADH为底物时SMPs的耗氧率更高，这表明SMPs依赖NADH与依赖琥珀酸的铬酸盐还原酶活性的差异可能是由于琥珀酸和NADH供电子效率的不同。使用特定的电子传递链抑制剂可以确定SMPs中六价铬还原和五价铬形成的位点。鱼藤酮、抗霉素和氰化物均对依赖NADH的铬酸盐还原酶活性产生约40%的抑制作用。因此，复合物I（NADH：泛醌氧化还原酶）似乎负责不敏感于抑制剂的反应，而复合物IV（亚铁细胞色素c：氧氧化还原酶）则负责对抑制剂敏感的依赖NADH的六价铬还原和五价铬形成。氰化物和抗霉素对SMPs依赖琥珀酸的铬酸盐还原酶活性产生约50%的抑制作用，而鱼藤酮未观察到可检测到的抑制作用。这些结果证实了复合物IV的铬酸盐还原酶活性，并表明复合物II（琥珀酸：泛醌氧化还原酶）负责SMPs中不敏感于抑制剂的依赖琥珀酸的铬酸盐还原酶活性。由于在体外六价铬可被线粒体内膜的电子传递链复合物有效代谢，且在此过程中会形成五价铬作为中间体，因此线粒体可能在六价铬致癌过程中发挥作用。
