Cytochrome P-450 from Bovine Adrenocortical Mitochondria: an Enzyme for the Side Chain Cleavage of Cholesterol

One mitochondrial cytochrome P-450 from bovine adrenal cortex is capable of catalyzing the conversion of cholesterol to pregnenolone (Shikita, M., and Hall, P. F. (1973) J. Biol. Chem. 248, 5598). This cytochrome (molecular weight, 850,000) was dissociated into subunits of molecular weight 53,000 in 6 m guanidine as demonstrated by sedimentation equilibrium analysis and by treatment with sodium dodecyl sulfate followed by electrophoresis on polyacrylamide gel. Sedimentation equilibrium in buffer of high ionic strength (µ = 0.23) revealed dissociation of the cytochrome into subunits of molecular weights of 470,000 and 200,000. It appears that this adrenocortical P-450 is isolated in a form consisting of 16 subunits and can exist in forms of 8 and 4 subunits; more drastic treatments result in the formation of monomer units. Maximal enzymatic activity is observed at an ionic strength (µ = 0.03 to 0.05) at which the enzyme is seen as protein 16 on analytical ultracentrifugation.