The roles of nadh in the support of steroid aromatization by human placental microsomes

• Published in: Steroids Vol. 42; no. 1; pp. 77 - 91
• Main Authors: Sheean, Leon A., Meigs, Robert A.
• Format: Journal Article
• Language: English
• Published: New York, NY Elsevier Inc 01.07.1983; Elsevier Science
• Subjects: Analytical, structural and metabolic biochemistry; Aromatase - metabolism; Biological and medical sciences; Female; Fundamental and applied biological sciences. Psychology; Glucosephosphate Dehydrogenase - metabolism; Humans; Kinetics; Leuconostoc - enzymology; Microsomes - metabolism; NAD - metabolism; NADPH-Ferrihemoprotein Reductase - metabolism; Other biological molecules; Oxidation-Reduction; Oxidoreductases - metabolism; Placenta - metabolism; Pregnancy; Terpenes, steroids. Hormones; Human; NADH; Placenta; Steroid hormone; Enzymatic system; Biosynthesis; Steroidogenesis; Microsome; Cofactor
• ISSN: 0039-128X; 1878-5867
• DOI: 10.1016/S0039-128X(83)90108-3

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 K m 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 K i values of 5 μM and 22 μM, 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.