INHIBITION BY CHOLESTEROL ANALOGUES OF SIDE-CHAIN CLEAVAGE OF CHOLESTEROL AND 20ALPHA-HYDROXYCHOLESTEROL IN A PREPARATION OF HOG ADRENOCORTICAL MITOCHONDRIA

1. Inhibitor specificity of the side-chain cleavage of cholesterol and 20α-hydroxy-cholesterol in a soluble preparation from hog adrenocortical mitochondria was examined.2. Strong inhibition of the cholesterol side-chain cleavage was observed by 3β-hydroxyl compounds, and moderate degree of inhibition was also shown by cholestenones. However, hydrogen at C-5 position and methyl groups at C-4 position modified the inhibitory activity of the compounds.3. No significant inhibition of cholesterol side-chain cleavage by cholesterol esters was noticed.4. Similar pattern of the inhibition of the side-chain cleavage of 20α-hydroxy-cholesterol was observed. However, the inhibition by 5-cholesten-3β-ol-7-one and cholestenone was significantly different from that of cholesterol side-chain cleavage.5. The inhibition of the side-chain cleavage of cholesterol and 20α-hydroxycholesterol by cholestarol and desmosterol was shown to be of a competitive type.6. Conversion of 414C-cholestenone into 14C-progesterone was detected in this enzyme system, whereas 414C-cholestanol was not cleaved to form 14C-5αpregnanolone.7. Properties of cholesterol and 20α-hydroxycholesterol side-chain cleaving enzyme system were discussed. © 1969 BY THE JOURNAL OF BIOCHEMISTRY.