Studies of the active site of cytochrome P-450scc with a high-affinity spin-labeled inhibitor.

The intramolecular site of P-450scc for conversion of cholesterol to pregnenolone involves a substrate site, an active site, and a site for transmission of electrons. The substrate site was studied with a high-affinity, high-potency nitroxide spin-labeled inhibitor of cholesterol side-chain cleavage. This substance, 17 alpha-hydroxy-11-deoxycorticosterone nitroxide (SL-V), has an affinity comparable to that of the most active substrate inhibitors ever reported and 2-50 times greater than that of the natural substrate cholesterol.

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.

Molecular interactions of progesterone analogues with rabbit uterine cytoplasmic receptor.

Binding energies of progesterone analogues with single modifications were calculated from their affinities for the cytosolic receptor of rabbit uteri. The effects of individual substituents were analyzed in terms of hydrogen bonds, van der Waals' forces, and hydrophobic interactions. Binding to the receptor is attributed to hydrogen bonds involving the ketones at carbons 3 and 20, and van der Waals' interactions at carbons 2, 4, 7, 9, 12, 18, and 19 at which positions the separation of the steroid from the receptor appears to be about 0.

Basic studies on aminoglutethimide.

Aminoglutethimide (AG), a bicyclic substance with two optically active isomers, inhibits the cholesterol side-chain cleavage (SCC) and aromatase systems by blocking the terminal cytochrome P-450s. AG interacts with these cytochromes to induce typical type II, low-spin spectra; the amount of spectral change correlates directly with the amount of enzymatic inhibition. AG acts by preventing reduction of the cytochrome, an obligate step preceding oxygenation of substrate.