The mechanism of C-4 demethylation during cholesterol biosynthesis. Evidence for a decarboxylation mechanism not involving a Schiff-base intermediate

The conversion of 4,4-dimethylcholest-7-enol into 4α-methylcholest-7-enol by rat liver microsomal preparations involves the decarboxylation of a sterol 3-oxo-4α-carboxylic acid. By using an ¹⁸O-labelled substrate it was shown that this decarboxylation does not involve a Schiff-base intermediate.