Chemical modification of cysteine residues of cholesterol-hydroxylating cytochrome P-450. Identification of the cysteine residue participating in the formation of a proximal ligand

A chemical modification of cysteine residues in mitochondrial cytochrome P-450scc from adrenal cortex has been carried out. Cysteine residues in this hemoprotein were shown to form two pools: one available to the chemical modification, which does not affect spectral and functional properties of the cytochrome and another accessible for the modification only after the protein inactivation and the heme removal. The proximal ligand in the polypeptide chain of cytochrome P-450scc was localized. Cys422 was shown to be involved in the heme coordination and Cys264 was found to be exposed and accessible to sulfhydryl reagents. The data obtained are discussed in terms of the functional role of cysteine residues in monooxygenase catalysis.