Abstract
Newly synthesized cytochrome P-450 was labeled by administration of radioactive δ-aminolevulinic acid to the rats prior to killing. Cytochrome P-450 fractions were isolated by solubilization of microsomes with sodium cholate followed by chromatography on octylamine-Sepharose and hydroxylapatite. The cholesterol 7α-hydroxylase activity was separated from the 5β-cholestane-3α,7α-diol, 12α, 25- and 26-hydroxylase activities. Cholesterol 7α-hydroxylase activity was found in a minor cytochrome P-450 fraction with low specific radioactivity. On the other hand, the 12α, 25- and 26-hydroxylase activities were found in a major cytochrome P-450 fraction with higher specific radioactivity. The results show that cholesterol 7α-hydroxylation is catalyzed by a cytochrome P-450 with short half-life and provide further evidence for the presence of a specific cytochrome P-450 species catalyzing the reaction.
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