Conversion of 7-alpha,12-alpha-dihydroxycholest-4-en-3-one to 5-alpha-cholestane-3-alpha, 7-alpha,12-alpha-triol by iguana liver microsomes.

The role of 7alpha,12alpha-dihydroxycholest-4-en-3-one as an intermediate in the formation of 5alpha-bile acids from cholesterol was investigated with liver preparations of Iguana iguana in vitro. The microsomal fraction of iguana liver catalyzed the transformation of 7alpha,12alpha-dihydroxycholest-4-en-3-one to 5alpha-cholestane-3alpha,7alpha,12alpha-triol in good yield. 7alpha,12alpha-dihydroxy-5alpha-cholestan-3-one served as an intermediate. Under the conditions employed, formation of the corresponding 5beta-isomers could not be detected. High speed supernatant solution and mitochondrial fraction of iguana liver did not reduce 7alpha,12alpha-dihydroxycholest-4-en-3-one to a measurable extent. The microsomal enzyme system required NADPH as hydrogen donor and was inactive in the presence of NADH. It is suggested that 7alpha,12alpha-dihydroxycholest-4-en-3-one may serve as a common intermediate in the formation of 5alpha- and 5beta-bile acids from cholesterol.