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.
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.