The role of mitochondrial cytochrome P 450 from bovine adrenal cortex in side chain cleavage of 20S,22R dihydroxycholesterol

The role of cytochrome P 450 in the side chain cleavage of 20S, 22R dihydroxycholesterol was investigated by examining the effect of carbon monoxide on the conversion of this substance to pregnenolone, by cytochrome P 450 from bovine adrenocortical mitochondria; the effect of carbon monoxide on the conversion of cholesterol to pregnenolone by the same enzyme also was examined. 50% inhibition of side chain cleavage was produced by gas mixtures with the following ratios: CO:O₂, 1.5 for cholesterol and 1.2 for 20S, 22R dihydroxycholesterol. Photochemical action spectra revealed that light of wavelength 451 nm decreased the inhibition of side chain cleavage of both substrates to a greater extent than light of other wavelengths. It is concluded that the heme moiety of P 450 is involved in the cleavage of 20S, 22R dihydroxycholesterol.