MODE OF ACTION OF FUNGICIDE DENMERT (S-1358) IN FUNGI .3. SELECTIVE-INHIBITION OF DEMETHYLATION AT C-14 IN ERGOSTEROL BIOSYNTHESIS BY FUNGICIDE, DENMERT (S-1358)

In cell-free homogenates of Saccharomyces cerevisiae, Denmert (S-1358) inhibited the incorporation of radioactivity from DL-mevalonate-2-14C into 14-desmethyl-lanosterol, 4.alpha.-methyl-cholesta-8,24-dien-3-one, 4.alpha.-methyl-zymosterol and 4-desmethyl sterols (zymosterol and episterol) at a concentration of 10-4 M. Concomitantly, a large accumulation of radioactivity was observed in the lanosterol fraction. In good agreement with results described above, Denmert inhibited the conversion of 14C-labeled lanosterol to 4-desmethyl sterols, while the conversion of 14C-labeled 14-desmethyl-lanosterol to 4-desmethyl sterols was hardly affected by the fungicide. It is evident that Denmert is a potent selective inhibitor of the demethylation at the C-14 position in ergosterol biosynthesis. The fungicide, triarimol, was found to exhibit the same effect on sterol biosynthesis as Denmert.