NOVEL STEROL TRANSFORMATIONS PROMOTED BY SACCHAROMYCES-CEREVISIAE STRAIN GL7 - EVIDENCE FOR 9-BETA,19-CYCLOPROPYL TO 9(11)-ISOMERIZATION AND FOR 14-DEMETHYLATION TO 8(14)-STEROLS

Cultures of Saccharomyces cerevisiae strain GL7 (a sterol auxotroph) w ere incubated with nonradioactive and tritium-labeled cycloartenol, an d the sterol composition of the cells was examined by chemical (GLC, T LC, HPLC, MS, H-1-NMR, and C-13-NMR) and radiotracer techniques. Sever al novel sterols were isolated from the cells including 14 alpha-methy ] ergosta-9(11),24(28)-dien-3 beta-ol, 24 beta-methyl-9 beta,19-cyclop ropyl ergost-8(14)-en-3 beta-o1, and 9 beta,19-cyclopropyl ergosta-7(8 ),24(28)-dien-3 beta-ol. GL7 converted [2-H-3]cycloartenol to [2-H-3]e rgosterol in low yield (1% incorporation), whereas [2-H-3]lanosterol w as converted to [2-H-3]ergosterol in high yield (41% incorporation). T he degree of sterol absorption and transformation by GL7 was dependent on the type and amount of sterol(s) in the growth medium. The results demonstrate for the first time that yeast may transform 9 beta,19-cyc lopropyl sterols to 9(11)-sterols and Delta(5)-sterols and that 14-dem ethylation of sterols may proceed in GL7 to double bond formation eith er in the 8(14)-position or in the 14(15)-position. (C) 1995 Academic Press, Inc.