A possible role for cytochrome P-450 during the biosynthesis of zymosterol from lanosterol by Saccharomyces cerevisiae

A cell-free system has been obtained from $\text{Saccharomyces cerevisiae}$ which is capable of efficiently converting lanosterol¹ to a mixture of 4-demethyl sterols, quantitatively the most important identifiable component of which was zymosterol. Little or no ergosterol was synthesized. In the presence of carbon monoxide, the rate of zymosterol biosynthesis from lanosterol was decreased by 57% compared with that observed in control incubations and the amount of unmetabolized lanosterol was greater. Mitochondrial electron transport inhibitors such as cyanide and antimycin A had no effect on the overall rate of 4-demethyl sterol biosynthesis from lanosterol nor on the degree of inhibition by carbon monoxide.