title: The roles of NADH in the support of steroid aromatization by human placental microsomes.
abstract: The ability of NADH to function as an alternative cofactor for the support of estrogen biosynthesis was validated. NADH supported rates of aromatization of up to 80% of those obtained with NADPH, with an apparent Km of 0.70 mM, and stimulated the NADPH-supported reaction only when supplies of the normal cofactor were limiting, both additive and synergistic effects being observed. NADH-supported aromatization was inhibited competitively by NADP+ and 2'-AMP with Ki values of 5 microM and 22 microM, respectively. Support by both cofactors was lost in parallel with the selective removal of NADPH-cytochrome c reductase from microsomes by graded subtilisin treatment. NADH-supported aromatization was differentiated from NADPH-supported aromatization by its sensitivity to inhibition by NAD+ and its response to changes in ionic strength. NADH appears to function, at high concentrations, as a surrogate for NADPH at the reduced nucleotide-binding site of NADPH-cytochrome c reductase but additional roles for NADH are also suggested both when acting alone and as a supplement to NADPH. A common oxidase (cytochrome P-450) appears to catalyze both NADH- and NADPH-supported aromatization.
mesh_terms: D001141:Aromatase / Q000378:metabolism*; D005260:Female; D005954:Glucosephosphate Dehydrogenase / Q000378:metabolism; D006801:Humans; D007700:Kinetics; D007934:Leuconostoc / Q000201:enzymology; D008861:Microsomes / Q000378:metabolism*; D009243:NAD / Q000378:metabolism*; D009251:NADPH-Ferrihemoprotein Reductase / Q000378:metabolism; D010084:Oxidation-Reduction; D010088:Oxidoreductases / Q000378:metabolism*; D010920:Placenta / Q000378:metabolism*; D011247:Pregnancy
chemical_list: D009243:NAD; D010088:Oxidoreductases; D005954:Glucosephosphate Dehydrogenase; D001141:Aromatase; D009251:NADPH-Ferrihemoprotein Reductase