title: Differential inhibition of androst-4-en-3,17-dione aromatization by carbon monoxide in the presence of estr-4-en-3,17-dione.
abstract: The aromatization of androst-4-en-3,17-dione or 17beta hydroxyandrost-4-en-3-one (testosterone) is not inhibited by carbon monoxide under normal incubation conditions, whereas the aromatization of corresponding 19-nor steroids (estr-4-en-3,17-dione and 17beta-hydroxyestr-4-en-3-one) is readily inhibited under the same conditions. A possible explanation was found when it was shown that androst-4-en-3,17-dione and testosterone could displace bound carbon monoxide from human placental microsomal cytochrome P-450. The 19-nor steroids did not displace carbon monoxide, even at very high concentrations. These C-18 compounds appeared to facilitate complex formation and reversed the effects of the C-19 steroids. A mutual antagonism was observed with regard to effects on the formation of the ce titrated. These observations suggested that the aromatization of androst-4-en-3,17-dione should be inhibited by carbon monoxide if sufficient concentrations of the 19-nor steroids were present in reaction flasks. This hypotheses was tested and positive results were obtained, providing strong evidence for the involvement of cytochrome P-450 in normal estrogen biosynthesis.
mesh_terms: D000735:Androstenedione / Q000378:metabolism* / Q000494:pharmacology; D001665:Binding Sites; D002248:Carbon Monoxide / Q000494:pharmacology*; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism; D004963:Estrenes / Q000494:pharmacology*; D005260:Female; D006801:Humans; D008861:Microsomes / Q000187:drug effects / Q000378:metabolism*; D010920:Placenta / Q000378:metabolism*; D011247:Pregnancy; D011485:Protein Binding
chemical_list: D004963:Estrenes; D000735:Androstenedione; D002248:Carbon Monoxide; D003577:Cytochrome P-450 Enzyme System