Quantitative effects of unsaturated fatty acids in microbial mutants. IV. Lipid composition of Saccharomyces cerevisiae when growth is limited by unsaturated fatty acid supply.

The Saccharomyces cerevisiae mutant KD46 (ole 2), which is unable to synthesize unsaturated fatty acids, was grown on limiting amounts of different added unsaturated fatty acids. The acyl chain composition of the cellular lipid classes was determined in these cultures at different stages or growth. During growth on added oleic acid, there was no marked change in the mole percentage of phosphatidylcholine, phosphatidylethanolamine. phosphatidylinositol, or phosphatidylserine among the total phospholipids. Cells grown on palmitoleic, oleic, or linoleic acid showed a steady decrease in their total phospholipid levels per cell concomitant with a decrease in growth rate approaching minimal levels at stationary phase. Furthermore, the mole percentage of the supplemented unsaturated fatty acid in the cellular phospholipids also decreased during growth and attained minimal values when growth ceased. At stationary phase the total phospholipid content per cell was similar for cells grown on a wide range of fatty acids or mixtures thereof, whereas the composition of the fatty acids in the cellular phospholipids were strikingly different. The differences in efficiencies for supporting growth of most of the unsaturated fatty acids tested did not seem due to the extent of their corporation into cellular phospholipids, but rather to differences in the ability of the derived membrane phospholipids to support cellular functions. Palmitoleate, oleate, linoleate, linolenate, arachidonate, eicosapentaenoate, and docosahexaenoate all appeared to contribute to the functionality of cellular membranes in an additive linear manner. Thus, the contribution of these acids to cellular growth can be characterized by a functionality factor that seems independent of the mixtures of acids supporting growth. Use of the functionality concept allows the cumulative influence of many different acids to be summarized quantitatively by a single number rather than resorting to qualitative decriptions of the degree of unsaturation or 'fitness' of the membrane phospholipids.