Reserve carbohydrate metabolism in Saccharomyces cerevisiae: responses to nutrient limitation

Abstract

The amounts of glycogen and trehalose have been measured in cells of a prototrophic diploid yeast strain subjected to a variety of nutrient limitations. Both glycogen and trehalose were accumulated in cells deprived specifically of nitrogen, sulfur, or phosphorus, suggesting that reserve carbohydrate accumulation is a general response to nutrient limitation. The patterns of accumulation and utilization of glycogen and trehalose were not identical under these conditions, suggesting that the two carbohydrates may play distinct physiological roles. Glycogen and trehalose were also accumulated by cells undergoing carbon and energy limitation, both during diauxic growth in a relatively poor medium and during the approach to stationary phase in a rich medium. Growth in the rich medium was shown to be carbon or energy limited or both, although the interaction between carbon source limitation and oxygen limitation was complex. In both media, the pattern of glycogen accumulation and utilization was compatible with its serving as a source of energy both during respiratory adaptation and during a subsequent starvation. In contrast, the pattern of trehalose accumulation and utilization seemed compatible only with the latter role. In cultures that were depleting their supplies of exogenous glucose, the accumulation of glycogen began at glucose concentrations well above those sufficient to suppress glycogen accumulation in cultures growing with a constant concentration of exogenous glucose. The mechanism of this effect is not clear, but may involve a response to the rapid rate of change in the glucose concentration.

Multiple regulatory mechanisms control the expression of the RAS1 and RAS2 genes of Saccharomyces cerevisiae.

“….fla: 00 * Nitrogen and sulfur starvation. Cells were grown to early-exponential phase in MIN medium (Lillie and Pringle, 1980) containing 2% glucose at 30°C, then shifted to nitrogenor sulfur-deficient MIN medium and cultured for 1_ up to 24 h. After 2 or 6 h, the missing nutrient was added to half of the culture. Growth and terminal phenotype of the cells were assessed as described above.…”

Does a cyclic AMP‐dependent phosphorylation initiate the transfer of trehalase from the cytosol into the vacuoles in Saccharomyces cerevisiae?

“…Saccharomyces cerevisiae (strain C 276 a/a, obtained from Dr J. Pringle; for trehalase metabolism, see [5]), was grown and protoplasts were prepared as in [1,6].…”

Deletion of the ATH1 gene in Saccharomyces cerevisiae prevents growth on trehalose

“…utilization Trehalose is a widely distributed carbohydrate in nature which is synthesized in S. cerevisiae in response to nutrient limitation and during certain environmental stress [19][20][21][22]. Ex-perimental evidence has shown that trehalose biosynthesis in yeast is catalyzed by the trehalose synthase complex [23,24], while its endogenous intracellular hydrolysis is catalyzed by the neutral trehalase but not the acid trehalase nor Ybr0106p (Nth2p) [6,10,11].…”