Testicular sterols

Homogenate of rate testicular tissue (10 000 × g for 20 min) was incubated with labeled lanosterol that was prepared biosynthetically from [2-¹⁴C]mevalonate. The oxidative demethylation of lanosterol to C₂₇ sterols was observed by the rate of release of labeled CO₂. No absolute requirement for added cofactors was demonstrated. The maximal rate of demethylation by testicular tissue was 4 mμmoles/h per 100 mg protein. The supernatant fraction from high-speed centrifugation of testicular tissue or liver supported the same rate of demethylation by liver microsomes. This rate was 6 times greater than the corresponding rate with testicular microsomes. In the presence of mitochondria, labeled CO₂ was liberated from lanosterol by both the demethylation reactions and by the oxidation of the side]hain fragment that is formed during the conversion of C₂₇ sterols to C₂₁ steroids. The rate of conversion of lanosterol to C₂₇ sterols and C₂₁ steroids was determined by difference. Inhibition of demethylation decreased the formation of steroids. The time-course of conversion of labeled lanosterol and [4-¹⁴C]cholesterol to testosterone and the effect of inhibition suggest that cholesterol or other C₂₇ sterols are biosynthetic intermediates between lanosterol and testosterone.