Differential dependence on NADPH concentrations of two microsomal corticosteroid 21-hydroxylation reactions.
The dependency on NADPH concentrations of the bovine adrenal cortex microsomal 21-hydroxylation of progesterone and of 17-hydroxyprogesterone was investigated. The average Km for NADPH in the 21-hydroxylation of progesterone is 10.4 muM while that for the 21-hydroxylation of 17-hydroxyprogesterone is 0.6 muM. The optimal NADPH concentrations for these two hydroxylations are, in average, one order of magnitude apart. The different affinities of the two 21-hydroxylating activities with respect to NADPH may indicate the presence of independent 21-hydroxylation reactions for these two steroid substrates. This evidence is consistent with the observed genetic data in human congenital adrenal hyperplasia.
D000302:Adrenal Cortex / Q000201:enzymology*; D000311:Adrenal Glands / Q000201:enzymology*; D000818:Animals; D001665:Binding Sites; D002417:Cattle; D006900:Hydroxylation; D006908:Hydroxyprogesterones / Q000378:metabolism*; D007700:Kinetics; D008861:Microsomes / Q000201:enzymology; D009249:NADP / Q000032:analysis*; D011374:Progesterone / Q000378:metabolism*; D013997:Time Factors
D006908:Hydroxyprogesterones; D011374:Progesterone; D009249:NADP