Inhibition of cholesterol side chain cleavage by active site directed antibody to corpus luteum cytochrome P-450.

Goat antibody IgG produced against bovine corpus luteum mitochondrial cytochrome P-450 (P-450scc) associated with cholesterol side chain cleavage (CSCC) was used to compare immunological characteristics of mitochondrial cytochrome P-450s from the bovine adrenal cortex (BAM), bovine corpus luteum (BCLM), and human placenta (HPM). In Ouchterlony double diffusion, anti-P450scc produced a single band with BAM and BCLM P-450scc, but not with HPM P-450scc or BAM P-450 11 beta. Appropriate concentrations of this anti-P-450scc IgG inhibited the conversion of cholesterol to pregnenolone in BCLM and BAM preparations equivalently, but inhibition of placental P-450scc was considerably less. The addition of BCLM iron sulfur protein and iron sulfur protein reductase to HPM P-450scc increased CSCC approximately 5-fold. Under these conditions, anti-P-450scc inhibited CSCC in HPM. Solubilized and sonicated BCLM preparations were inhibited equivalently but more than whole mitochondria. Addition of anti-P-450scc IgG to BAM increased 11 beta-hydroxylation activity in concentration-dependent fashion. It appears that the cytochrome P-450sccs from BAM and BCLM are very similar if not identical, but immunologically different from HPM P-450scc. The BAM P-450 11 beta is immunochemically distinct from BCLM P-450scc. The CSCC and 11 beta-hydroxylation systems of the adrenal are intimately linked because inhibition of P-450scc markedly stimulated 11 beta-hydroxylation. Finally, the inhibition of CSCC activity of BAM, BCLM, and HPM P-450 indicates that the antigenic effect is directed toward the active site.