Removal of the 4,4-Dimethyl Carbons in the Enzymic Conversion of Lanosterol to Cholesterol INITIAL LOSS OF THE 4α-METHYL GROUP

Abstract The sequence of removal of methyl substituents at C-4 of 4,4,14α-trimethyl-5α-cholesta-8,24-dien-3β-ol (lanosterol) in the course of its conversion to cholesterol has been re-examined. From a homogenate of rat liver incubated with dl-mevalonic acid-2-14C-5-3H, squalene, lanosterol, 4,4,14α-trimethyl-5α-cholest-8-en-3β-ol, 4α-methyl-5α-cholest-7-en-3β-ol, and cholesterol have been isolated. It is concluded from measurements of the 3H:14C ratios found in these various compounds that the 4α-methyl group of lanosterol is removed before the 4β-methyl group and that the 4α-methyl group of 4α-methyl-5α-cholest-7-en-3β-ol originates as the 4β-methyl group of lanosterol.