Cholesterol Side Chain Cleavage Cytochrome P450 (P450scc)

Cytochrome P450scc (CYPllA1) catalyzes the initial step in the biosynthesis of steroid hormones, the conversion of cholesterol to pregnenolone. This is the rate-determining step in the synthetic pathway and is a key site of regulation (Stone and Hector 1955; Koritz and Kramer 1970). Cytochrome P450scc is found at high levels in steroidogenic tissues, most notably the adrenal cortex, ovary, testes, and placenta, and is localized in the inner mitochondrial membrane (Churchill et al. 1978; Mitani et al. 1982). The enzymology, cellular regulation, and molecular biology of cytochrome P450scc have been extensively studied, and several comprehensive reviews can be found in chapters of a recent treatise on steroid biogenesis (cf. Usanov et al. 1990; Lambeth 1990; Waterman and Simpson 1990)