CONTROL OF FATTY-ACID SYNTHETASE LEVELS BY EXOGENEOUS LONG-CHAIN FATTY-ACIDS IN YEASTS CANDIDA-LIPOLYTICA AND SACCHAROMYCES-CEREVISIAE

Endogeneous fatty acid biosynthesis in the 2 yeast species, S. cerevisiae and C. lipolytica is completely repressed by the addition of long-chain fatty acids to the growth medium. In C. lipolytica, this repression is accompanied by a corresponding loss of fatty acid synthetase activity in the cell homogenate, when the cells were grown on fatty acids as the sole carbon source. The activity of the S. cerevisiae fatty acid synthetase, however, remains unaffected by the addition of fatty acids to a glucose-containing growth medium. From fatty-acid-grown C. lipolytica cells no fatty acid synthetase complex can be isolated, nor is there any immunologically cross-reacting fatty acid synthetase protein detectable in the crude cell extract. C. lipolytica, but not S. cerevisiae, is probably able to adapt to the growth on fatty acids either by repression of fatty acid synthetase biosynthesis or by a fatty-acid-induced proteolytic degradation of the multienzyme complex. Similarly, the fatty acid synthetase complex disappears rapidly from stationary phase C. lipolytica cells even after growth in fatty-acid-free medium. The fatty acid synthetase complexes from S. cerevisiae and C. lipolytica, though very similar in size and subunit composition, were immunologically different and had no common antigenic determinants.