Effect of unsaturated fatty acids on the biosynthesis of glucose-repressed enzymes in yeast

In anaerobically glucose-grown yeast isocitrate lyase (EC 4.1.3.1.), malate synthase (EC 4.1.3.2.) and malate dehydrogenase (EC 1.1.1.37.) are repressed by glucose. 24 h cultures still contain 0.3–0.4% glucose in the medium, which is enough to completely repress these activities. Aeration of these cells, in buffer containing acetate, initiates the formation of the three enzymes. Within 16 h, the specific activities of these enzymes increase about 140, 120 and 70-fold, respectively. Glucose-6-phosphate dehydrogenase activity was not altered. When the yeast was grown anaerobically, but with a supplement of an unsaturated fatty acid in the medium, synthesis of the three enzymes was much faster and the specific activities after 16 h of derepression were considerably higher. A relationship exists between the number of double bonds in the unsaturated fatty acid molecule and its capability to stimulate enzyme synthesis: linolenic acid is more effective than linoleic acid, which, in turn, is much more effective than oleic acid. Increasing periods of aeration with glucose of anaerobically grown cells prior to derepression results in an increasing stimulation of enzyme synthesis on subsequent derepression. Anaerobic incubation of yeast in the presence of an unsaturated fatty acid in advance to derepression also increased the velocity of enzyme formation. It is suggested that during the aeration period with glucose and during anaerobic incubation with an unsaturated fatty acid a more active protein synthesizing apparatus was formed.