6. Steroid metabolism in neuroendocrine structures. Specific and nonspecific components in the oxidative metabolism of estradiol by the male rat brain in vitro.
The oxidative transformation of estradiol at the C-2 and C-4 positions in the male rat brain was studied by the transfer of 3H into water from [2-3H]- and [4-3H]-estradiol. The nonenzymatic transformation at either site was linear with substrate concentration. The addition of pyridine nucleotide cofactors had no effect on the transformation at the C-4 site. The C-2 reaction was greatly enhanced by NADPH or NADH and exhibited the greatest velocity in the microsomal formation in the presence of NADH. The C-2 reaction exhibited saturation with respect to substrate and NADH with apparent KM of 1.82 microM and 0.34 mM respectively and Vmax of 81.3-76.3 pmol/mg protein/60 min. The reaction at C-4 failed to exhibit substrate saturation up to 30 microM. These data indicate that male rat brain estrogen hydroxylase is specific for the C-2 position, is NADH dependent and thus different from the corresponding liver enzyme. The reaction at C-4 in the brain tissues fails to exhibit enzymatic characteristics and the formation of 4-hydroxyestrogens in that tissue may be artifactual.
D000818:Animals; D001711:Biotransformation; D001921:Brain / Q000187:drug effects / Q000378:metabolism*; D002248:Carbon Monoxide / Q000494:pharmacology; D004958:Estradiol / Q000378:metabolism*; D007700:Kinetics; D008297:Male; D008861:Microsomes / Q000378:metabolism; D009243:NAD / Q000378:metabolism; D009249:NADP / Q000378:metabolism; D010084:Oxidation-Reduction; D051381:Rats; D014316:Tritium
D009243:NAD; D014316:Tritium; D004958:Estradiol; D009249:NADP; D002248:Carbon Monoxide