Yeast sterol esters and their relationship to the growth of yeast.

Variation in the percentage of sterols esterified to long-chain fatty acids during cellular growth has been examined. Under all conditions, a constant percentage of sterol esters was maintained during exponential growth. This maintenance level was found to vary with different growth conditions. A sharp increase in the rate of esterification was observed upon entry of the culture into the stationary growth phase. The minor cellular sterol components were found to accumulate after this period of rapid sterol ester synthesis, with a relative decrease in the size of the ergosterol pool. Evidence is presented that sterol esters of ergosterol precursors are unable to be metabolized to ergosterol. Once esterified, the fatty acids do not appear to be scavenged during starvation conditions.