PH-Dependent changes in the spin state of cytochrome P450 from adrenal mitochondria

Abstract

Cytochrome P450 in the adrenal cortex participates as a mixed function oxidase in several steps in the biosynthesis of corticosterone, of which side chain cleavage (XC) of cholesterol [l] and 1 l/3-hydroxylation of 1 1-deoxycorticosterone (1 I-DOC) occur in the mitochondria [2]. These two oxidations are specifically inhibited by aminoglutethimide and metapyrone [3] respectively, suggesting that different enzymes are involved in these oxidations. Recently the cytochrome P450 of adrenal mitochondria has been separated into two fractions which, with the same reducing system, specifically carry out 1 lh high spin (sm = 7.49) and low spin (sm = 2.45, g = 2.26, sm = 1.91) [5]. In addition, steroid-induced changes in the above EPR spectra and in the absorption spectra of the separated cytochrome P450 fractions [4] indicate that low spin 1 l/3-hydroxylase cytochrome P450 changes to a high spin state binding 1 l-DOC, while high spin SCCP450 is converted to a low spin state by pregnenolone. In this paper we show that the spin state and ligand binding properties of the SCC-cytochrome P450, but not 1 l/3-hydroxylase cytochrome P450, are very sensitive to pH.