title: Cytochrome b5 promotes the synthesis of delta 16-C19 steroids by homogeneous cytochrome P-450 C21 side-chain cleavage from pig testis.
abstract: Conversion of progesterone to 17 alpha-hydroxyprogesterone plus androstenedione (17 alpha-hydroxylation) and to androstadienone (delta 16 synthetase activity) by microsomes from neonatal pig testis, were both inhibited by antibodies raised against homogeneous cytochrome P-450 C21 side-chain cleavage. Inhibition of the two activities showed the same relationship to the concentration of antibody added. Analogous results were obtained with pregnenolone as substrate. In a reconstituted enzyme system consisting of the homogeneous cytochrome P-450 C21 side-chain cleavage enzyme, P-450 reductase and NADPH, addition of cytochrome b5 resulted in the synthesis of the corresponding delta 16-C19-steroid from progesterone (androstadienone) and pregnenolone (androstadienol). The effect of cytochrome b5 was concentration-dependent and prevented by anti-cytochrome b5. It is concluded that the cytochrome P-450 C21 side-chain cleavage enzyme from pig testicular microsomes is also capable of synthesizing delta 16-C19-steroids and is, therefore, likely to be responsible for the large amounts of the pherormone androstadienone produced by male pigs.
mesh_terms: D000446:Aldehyde-Lyases / Q000302:isolation & purification / Q000378:metabolism*; D000730:Androstadienes / Q000096:biosynthesis; D000737:Androstenols / Q000096:biosynthesis; D000818:Animals; D003573:Cytochrome b Group / Q000378:metabolism*; D015786:Cytochromes b5; D008297:Male; D008861:Microsomes / Q000201:enzymology; D009097:Multienzyme Complexes / Q000378:metabolism*; D009249:NADP / Q000378:metabolism; D009251:NADPH-Ferrihemoprotein Reductase / Q000378:metabolism; D010088:Oxidoreductases / Q000378:metabolism*; D010675:Pheromones / Q000096:biosynthesis; D013254:Steroid 17-alpha-Hydroxylase; D013552:Swine
chemical_list: D000730:Androstadienes; D000737:Androstenols; D003573:Cytochrome b Group; D009097:Multienzyme Complexes; D010675:Pheromones; C000152:androsta-5,16-dien-3 beta-ol; C003524:4,16-androstadien-3-one; D009249:NADP; D015786:Cytochromes b5; D010088:Oxidoreductases; C019701:androsta-5,16-dien-3 beta-ol synthetase; D013254:Steroid 17-alpha-Hydroxylase; D009251:NADPH-Ferrihemoprotein Reductase; D000446:Aldehyde-Lyases