THE 4-BETA-METHYL GROUP OF SUBSTRATE DOES NOT AFFECT THE ACTIVITY OF LANOSTEROL 14-ALPHA-DEMETHYLASE (P-45014DM) OF YEAST - DIFFERENCE BETWEEN THE SUBSTRATE RECOGNITION BY YEAST AND PLANT STEROL 14-ALPHA-DEMETHYLASES

Interaction of obtusifoliol and 24,28-dihydroobtusifoliol with yeast lanosterol 14a-demethylase (P-45014dm) was studied to elucidate the role of the 4β-methyl group of substrate. P-45014dm of Saccharomyces cerevisiae catalyzed 14α-demethylation of obtusifoliol. Apparent Vmax of obtusifoliol demethylation (15.4 nmol/min/nmol P-450) was similar to that of 24-methylene-24,25-dihydrolanosterol demethylation and was a little higher than those of lanosterol and 24,25-dihydrolanosterol demethylations. Apparent Km for obtusifoliol (12.0 μM) was higher than those for lanosterol and 24-methylene-24,25-dihydrolanosterol but was lower than that for 24,25-dihydrolanosterol. 24,28-Dihydroobtusifoliol was a very poor substrate for yeast P-45014dm. These facts suggest that the 413-methyl group of sterol slightly affects the activity of yeast P-45014dm, while hydrogenation of a double bond in the sterol side-chain considerably impairs the activity. This finding is a contrast to the fact that the plant P-45014dm could not catalyze demethylation of sterols having 4β-methyl group, but favorably interacts with sterols having saturated side chain. © 1992 Academic Press, Inc.