Inhibition of iron-sulfur protein-mediated reduction of cytochrome P-450SCC by specific antibodies.
The mechanism of inhibition of cholesterol side-chain cleavage by specific antibodies was studied systematically. The antibodies had no effect on substrate binding as determined by optical spectroscopy or on the heme environment of the cytochrome P-450 insofar as was detectable by electron paramagnetic resonance spectroscopy. They did not bind to either iron-sulfur protein or its reductase. The antibodies had no effect on chemical reduction of the P-450 or on P-450-CO complex formation. They did inhibit the NADPH-dependent reduction of P-450 and subsequent formation of the P-450-CO complex. This inhibitory effect was concentration dependent and was correlated with the inhibitory effect of the antibodies on enzymatic cholesterol side-chain cleavage. Similar results were obtained using Fab fragments. These results indicate that the antibodies inhibit side-chain cleavage by binding to a region close to the iron-sulfur protein-binding site, thereby preventing transfer of reducing electrons to the cytochrome P-450.
D000616:Aminoglutethimide / Q000494:pharmacology; D000818:Animals; D000906:Antibodies / Q000276:immunology*; D001665:Binding Sites; D002417:Cattle; D002784:Cholesterol / Q000378:metabolism*; D003577:Cytochrome P-450 Enzyme System / Q000276:immunology / Q000378:metabolism*; D004579:Electron Transport; D066298:In Vitro Techniques; D007506:Iron-Sulfur Proteins / Q000378:metabolism*; D008667:Metalloproteins / Q000378:metabolism*; D009249:NADP / Q000494:pharmacology; D010084:Oxidation-Reduction
D000906:Antibodies; D007506:Iron-Sulfur Proteins; D008667:Metalloproteins; D000616:Aminoglutethimide; D009249:NADP; D003577:Cytochrome P-450 Enzyme System; D002784:Cholesterol