Following separation of the seminiferous tubules from the interstitial cells in the rat testis, the amount of cytochrome P-450 and the activities of the cytochrome P-450-dependent enzymes, the 17alpha-hydroxylase and the C17-C20 lyase, were measured in the microsomes of the separated fractions. The amount of cytochrome P-450-dependent enzymes recovered in the microsomal fraction of the interstitial cells ranged from 71 to 86% of the whole testis. However, in some experiments lower recoveries of the activities of the enzymes were attributed to the breakdown of cytochrome P-450 to cytochrome P-420. In all cases, less than 10% of the testicular cytochrome P-450 and the cytochrome P-450-dependent steroidogenic enzymes were found in the tubular microsomes. Moreover, the specific activities of the 17 alpha-hydroxylase and the C17-C20 lyase were found to be 10 to 30 times higher in the interstitial tissue than in the seminiferous tubules of the rat testis. From these results, we have concluded that cytochrome P-450 and the activities of the cytochrome P-450-dependent enzymes in the rat testis are predominantly, if not sole, located in the interstitial cells.
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