Participation of cytochrome P-450 in the steroid 17alpha-hydroxylase of testis microsomes.

The effect of metyrapone on the activity of the steroid 17alpha-hydroxylase from rat testis was evaluated. A competitive pattern of inhibition was observed after analysis of data using a least mean squares computer analysis. The substrate for the hydroxylase induced a Type I difference spectrum in an active suspension of Triton treated microsomes. The magnitude of this spectral change was dependent on steroid concentration and was diminished by metyrapone. The effect of metyrapone was abolished at infinite steroid concentration. These results confirm the participation of cytochrome P-450 as a reactant in the 17alpha-hydroxylase reaction.