Cytochrome b5 stimulates purified testicular microsomal cytochrome P-450 (C21 side-chain cleavage)

Abstract

Cytochrome b5 purified from neonatal pig testis and that from pig liver stimulated C21 steroid side-chain cleavage (progesterone → androstenedione) catalyzed in vitro by purified cytochrome P-450 from neonatal pig testicular microsomes. Km of testicular cytochrome b5 for the P-450 is 6.3–9.1 × 10−8M and the ability of b5 to stimulate C21 side-chain cleavage is different for cytochromes b5 prepared from different sources.