Influence of glutathione on the catalytic activity of reconstituted cytochrome P450 3A4

Abstract

The role of NADPH reductase and cytochrome b(5) on glutathione (GSH)-induced stimulation of P450 3A4 activity was investigated, GSH increased the V-max of testosterone GP-hydroxylation without changing the K-m for testosterone whereas it decreased the K-m for NADPH-P450 reductase, Addition of cytochrome b(5) 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 b(5), 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 b(5), but has no effect on the affinity between P450 3A4 and testosterone. (C) 1998 Academic Press.