Lanosterol 14alpha-demethylase. Similarity of the enzyme system from yeast and rat liver.

The chemical synthesis of 24,25-dihydro[32-14C]lanosterol is described. The incubation of this material with a cell-free system from Saccharomyces cerevisiae or with a microsomal preparation from rat liver resulted in both cases in the release of [14C]formic acid. This result suggests that in the biosynthesis of ergosterol in yeast, as well as in that of cholesterol in higher animals, the 14alpha-methyl group of lanosterol is removed as formic acid. In both systems, the measurement of the rate of release of [14C]formic acid from 24,25-dihydro[32-14C]lanosterol provides a simple and direct assay of lanosterol 14alpha-demethylase. Carbon monoxide inhibited both yeast and liver 14alpha-demethylase.