Conversion of 5β-cholestane-3α,7α,12α,26-tetrol into 3α,7α,12α-trihydroxy-5β-cholestanoic acid by rabbit liver mitochondria

Rabbit liver mitochondria in the presence of NAD + were found to catalyze the conversion of 5β-cholestane-3α,7α,12α,26-tetrol into 3α,7α,12α-trihydroxy-5β-cholestanoic acid. The peroxisomal fraction did not catalyze the reaction. Sonication of the mitochondria or dialysis overnight against a hypotonic buffer increased the rate of oxidation twofold. Most of the enzyme activity was recovered in the supernatant fraction after centrifugation at 100,000xg of sonicated mitochondria. 4-Heptylpyrazole, an inhibitor of cytosolic ethanol dehydrogenase, inhibited the mitochondrial formation of 3α,7α,12α-trihydroxy-5β-cholestanoic acid by 70%. Disulfiram, an inhibitor of cytosolic acetaldehyde dehydrogenase, did not inhibit the reaction. The role of the mitochondrial dehydrogenase system in bile acid biosynthesis is discussed.