Fatty‐Acid Elongation in a Mutant of Saccharomyces cerevisiae Deficient in Fatty‐Acid Synthetase

The incorporation and metabolic alteration of a variety of dietary fatty acids has been studied in wild‐type Saccharomyces cerevisiae and a fatty‐acid auxotroph which carries a genetic defect in its fatty‐acid synthetase complex. This mutant grows when supplemented with a singleven or odd chain‐length fatty acid ranging from 13–17 carbon atoms. Although incapable of fattyacid synthesis from acetate de novo, the mutant yeast still elongates the dietary fatty acids by one or more C2 units. The extent of elongation is dependent on the chain length of the fatty acid included in the growth medium. It is most evident with tridecanoic acid and insignificant with palmitic acid. All saturated fatty acids are desaturated to an appreciable but varying degree to the corresponding monounsaturated acids. No degradation to lower homologues is observed in the wild‐type, nor in the mutant cells. No evidence was obtained to indicate participation of the mutant fatty‐acid synthetase complex in the elongation process described. In wild‐type yeast, intracellular fatty acid biosynthesis is unimpaired by the addition of free fatty acids to the growth medium and apparently proceeds by a much faster rate than the uptake and elongation of fatty acids from the growth medium. A membrane‐bound enzyme analogous to acid : CoA ligase has been isolated from bakers' yeast and its chain‐length specificity studied. The optimal chain length with saturated fatty acids is 15 carbon atoms. Unsaturated fatty acids are generally better substrates. The role of fatty acid activation in determining the rate of fatty‐acid‐dependent yeastmutant growth is discussed.