Spectral Evidence for a Liver Mitochondrial Cytochrome P450 Involved in Bile Acid Metabolism

Abstract
Optical difference spectroscopy of liver mitochondria has revealed the presence of a cytochrome P450 species by its ligand reactions with CO, metyrapone and diethylphenylphosphine. Its concentration of 0.15 nmol/mg mitochondrial protein is high enough to be detectable by ESR. A microsomal contamination of the mitochondria could be excluded. Mitochondrial cytochrome P450 forms an enzyme-substrate complex with 5.beta.-cholestane-3.alpha.,7.alpha.,12.alpha.-triol with Ks value very similar to the Km value of the 26-hydroxylation of this substrate. This supports the existence in liver mitochondria of a cytochrome P450-dependent 26-monooxygenase for bile acid precursors on the basis of a photochemical action spectrum.