IDENTIFICATION OF 24-METHYLENE-24,25-DIHYDROLANOSTEROL AS A PRECURSOROF ERGOSTEROL IN THE YEASTS SCHIZOSACCHAROMYCES-POMBE AND SCHIZOSACCHAROMYCES-OCTOSPORUS

Study of the plasma membrane sterol composition in the yeasts Schizosa ccharomyces pombe and Schizosaccharomyces octosporus revealed the pres ence of ergosterol, lanosterol, dehydroergosterol, fecosterol, epister ol and 24-methylene-24,25-dihydrolanosterol (eburicol), a C-31 derivat ive. The growth of both yeasts in the presence of ketoconazole led to a decrease by 85% of the ergosterol content while the levels of lanost erol and eburicol increased. This suggests that in the biosynthetic pa thway of ergosterol in Schizosaccharomyces species, the transmethylati on process on the C-24 may occur directly on lanosterol and not only o n zymosterol. On the other hand, it cannot be excluded that in the gen us Schizosaccharomyces two routes exist from lanosterol to ergosterol: the classical one via a direct C-14, C-4 demethylation of lanosterol and the second one via the formation of a C-31 derivative followed by demethylations.