Inhibitory effect and interaction of stanozolol with pig testicular cytochrome P-450 (17.ALPHA.-hydroxylase/C17.20-lyase).

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Abstract
The inhibitory effect on an anabolic steroid, stanozolol, on testicular microsomal cytochrome P-450 (17.alpha.-hydroxylase/C17,20-lyase) (P-45017.alpha.lyase) and the nature of the interaction were compared with those of other anabolic steroids, furazabol and mestanolone. Stanozolol markedly inhibited .DELTA.16-C19-steroid synthesizing activity. 17.alpha.-hydroxylase and C17,20-lyase activities, which were mediated by oxygenase activities of testicular microsomal cytochrome P-45017.alpha./lyase. In addition, stanozolol was a competitive inhibitor of 17.alpha.-hydroxylase (Ki = 6.31 .mu.M) and C17,20-lyase (Ki = 1.30 .mu.M) activities in the reconstituted enzyme system. The interaction of cytochrome P-45017.alpha./lyase with stanozolol induced a type I difference spectrum (peak at 387 nm and trough at 418 nm) with a dissociation constant (KS) of 1.47 .mu.M.