The Effects of Catabolite Derepression on the Accumulation of Steryl Esters and the Activity of -Hydroxymethylglutaryl-CoA Reductase in Saccharomyces cerevisiae

The transition from the fermentative mode of growth on glucose to the oxidative mode of growth on ethanol by Saccharomyces cerevisiae is accompanied by many changes collectively known as catabolite derepression. Catabolite derepression caused a progressive increase in the total content of cellular sterols, amounting to a fourfold increase after 8 h; the additional sterols existed almost entirely as esters of monoenoic fatty acids. The increase in sterol content could be explained by the large increase in the activity of β-hydroxymethylglutaryl-CoA reductase (EC 1.1.1.34), but a secondary factor in sterol accumulation may have been the slower rate of cell growth during ethanol oxidation. Subsequent anaerobic growth of derepressed cells resulted in the hydrolysis of steryl esters to free sterols, and a progressive depletion of cellular sterol content.