Phospholipid synthesis in S. cerevisiae strain GL7 grown without unsaturated fatty acid supplements.

In the absence of exogenous unsaturated fatty acids (UFA), Saccharomyces cerevisiae strain GL7 synthesizes low levels of UFA and large amounts of decanoic, dodecanoic and tetradecanoic fatty acids. Supplementation with hemin leads to slightly higher levels of UFA, but synthesis of the medium-chain saturated fatty acids (SFA) continues. Under these conditions of limited UFA availability, strain GL7 incorporates most of its UFA into phosphatidylethanolamine (PE), whereas phosphatidylcholine (PC) and phosphatidylserine + phosphatidylinositol (PS+PI) are enriched with the medium-chain SFA. The association of specific fatty acids with the various phospholipids is not accompanied by changes in the proportions of newly synthesized phospholipids, demonstrating that the fatty acid composition of PE can be modulated independently of the other phospholipids. The effect of sterol structure on the fatty acid composition of cells grown with limiting UFA was also examined. Yeast cells grown with either ergosterol or stigmasterol contained less UFA and more medium-chain SFA in their phospholipids than did cholesterol-grown cells, suggesting that the former sterols allow strain GL7 to grow with a lower UFA content.