Kim B R, Kim D H
Department of Biochemistry, School of Medicine, Won Kwang University, Iksan, Korea.
Biochem Biophys Res Commun. 1998 Jan 6;242(1):209-12. doi: 10.1006/bbrc.1997.7861.
The role of NADPH reductase and cytochrome b5 on glutathione (GSH)-induced stimulation of P450 3A4 activity was investigated. GSH increased the Vmax of testosterone 6 beta-hydroxylation without changing the K(m) for testosterone whereas it decreased the K(m) for NADPH-P450 reductase. Addition of cytochrome b5 inhibited testosterone 6 beta-hydroxylation in the reconstituted system, depleting GSH, while it dramatically enhanced the rate of testosterone 6 beta-hydroxylation in the presence of GSH. Cumene hydroperoxide-mediated P450 3A4 activity, which is independent of NADPH-P450 reductase and cytochrome b5, was not affected by GSH. High concentration of GSH above 4 mM was inhibitory in the reconstituted systems. These results suggest that GSH increases the apparent affinity between P450 3A4 and NADPH-P450 reductase, and between P450 3A4 and cytochrome b5, but has no effect on the affinity between P450 3A4 and testosterone.
研究了NADPH还原酶和细胞色素b5在谷胱甘肽（GSH）诱导的细胞色素P450 3A4（CYP3A4）活性刺激中的作用。GSH增加了睾酮6β-羟化的最大反应速度（Vmax），而不改变睾酮的米氏常数（Km），但降低了NADPH-P450还原酶的Km。添加细胞色素b5在重组体系中抑制了睾酮6β-羟化，消耗了GSH，而在有GSH存在时显著提高了睾酮6β-羟化的速率。异丙苯过氧化氢介导的CYP3A4活性独立于NADPH-P450还原酶和细胞色素b5，不受GSH影响。在重组体系中，高于4 mM的高浓度GSH具有抑制作用。这些结果表明，GSH增加了CYP3A4与NADPH-P450还原酶之间以及CYP3A4与细胞色素b5之间的表观亲和力，但对CYP3A4与睾酮之间的亲和力没有影响。
