Roy D, Strobel H W, Liehr J G
Department of Pharmacology and Toxicology, University of Texas Medical Branch, Galveston 77550.
Arch Biochem Biophys. 1991 Mar;285(2):331-8. doi: 10.1016/0003-9861(91)90368-s.
Previously, we have demonstrated microsomal cytochrome P450-catalyzed redox cycling of estrogens. In this study, we investigated the role of cytochrome b5 in redox cycling in order to obtain a full understanding of enzymatic contributions to redox reactions of estrogens. Pure cytochrome P450c and hydrogen peroxide or cumene hydroperoxide oxidized diethylstilbestrol (DES) to diethylstilbestrol-4',4"-quinone (DES Q). This oxidation by H2O2 was doubled by addition of cytochrome b5 to cytochrome P450c (molar ratio of 1:4), but did not proceed with cytochrome b5 alone. The stimulation by cytochrome b5 of the cytochrome P450c-catalyzed oxidation of DES to DES Q occurred via modulation of the Vmax of cytochrome P450c rather than of the Km. DES Q was reduced to DES by purified cytochrome b5 and NADH-dependent cytochrome b5 reductase. Pretreatment of microsomes with an antibody to cytochrome b5 reductase inhibited microsomal NADH-dependent reduction of DES Q to DES by 55%. Cytochrome b5 likely participates in the oxidation of DES to DES Q by interacting with cytochrome P450c and in the reduction of DES Q to DES by interacting with cytochrome b5 reductase. Thus, the study demonstrates that cytochrome b5 plays an active role in biological oxidation and reduction reactions.
此前，我们已经证明微粒体细胞色素P450催化雌激素的氧化还原循环。在本研究中，我们研究了细胞色素b5在氧化还原循环中的作用，以便全面了解酶对雌激素氧化还原反应的贡献。纯细胞色素P450c与过氧化氢或氢过氧化异丙苯可将己烯雌酚（DES）氧化为己烯雌酚-4',4''-醌（DES Q）。向细胞色素P450c中添加细胞色素b5（摩尔比为1:4）后，H2O2介导的这种氧化作用增强了一倍，但单独使用细胞色素b5时该氧化反应不发生。细胞色素b5对细胞色素P450c催化的DES氧化为DES Q的刺激作用是通过调节细胞色素P450c的Vmax而非Km来实现的。纯化的细胞色素b5和NADH依赖性细胞色素b5还原酶可将DES Q还原为DES。用细胞色素b5还原酶抗体预处理微粒体可使微粒体中NADH依赖性的DES Q还原为DES的反应受到55%的抑制。细胞色素b5可能通过与细胞色素P450c相互作用参与DES氧化为DES Q的过程，并通过与细胞色素b5还原酶相互作用参与DES Q还原为DES的过程。因此，该研究表明细胞色素b5在生物氧化和还原反应中发挥着积极作用。
