Regulation of trehalose mobilization in fungi.

Catabolite inactivation in yeast

Transport of sugars is a fundamental property of all eukaryotic cells. Of particular importance is the uptake of glucose, a preferred carbon and energy source. The rate of glucose utilization in yeast is often dictated by the activity and concentration of glucose transporters in the plasma membrane. Given the importance of transport as a site of control of glycolytic flux, the regulation of glucose transporters is necessarily complex. The molecular analysis of these transporters in Saccharomyces has revealed the existence of a multigene family of sugar carriers. Recent data have raised the question of the actual role of all of these proteins in sugar catabolism, as some appear to be lowly expressed, and point mutations of these genes may confer pleiotropic phenotypes, inconsistent with a simple role as catabolic transporters. The transporters themselves appear to be intimately involved in the process of sensing glucose, a model for which there is growing support.

Yeast Sugar Transporters

Publisher Summary This chapter reviews the role of peroxisomes in the metabolism of methanol and methylated amines in yeasts. It provides information regarding their biogenesis and turnover. The studies on the physiology and biochemistry of methanol oxidation by methylotrophic yeasts exhibit that adaptation of these organisms to growth on methanol is associated with the proliferation of large microbodies in the cells. To evaluate the unique function and structure of the microbodies during methylotrophic growth in yeasts it is necessary to consider pertinent biochemical and physiological aspects of methanol metabolism in these organisms. Microbodies of methanol-grown yeasts show a number of characteristic properties.They appear in clusters in the cell and exist in close association with strands of endoplasmic reticulum. Evidence that the microbodies of methanol-grown yeasts contain alcohol oxidase and catalase is obtained via cell fractionation and cytochemical studies. The information on various aspects of the role of peroxisomes in the metabolism of one-carbon compounds in yeasts clearly shows that these unicellular organisms offer an almost ideal model system for the study of function, morphogenesis, and turnover of these intriguing organelles.

The Significance of Peroxisomes in the Metabolism of One-Carbon Compounds in Yeasts

Mutants have been isolated in S. cerevisiae with the phenotype of growth on pyruvate but not on glucose, or growth on rich medium with pyruvate but inhibition by glucose. Screening of mutagenized cultures was either without an enrichment step, or after enrichment using the antibiotic netropsin (Young et al. 1976) or inositol starvation ( Henry, Donahue and Culbertson 1975). One class of mutants lacked pyruvate kinase (pyk), another class had all the enzymes of glycolysis, and one mutant lacked phosphoglucose isomerase (pgi, Maitra 1971). Partial reversion of pyruvate kinase mutants on rich medium containing glucose gave double mutants now also lacking hexokinase (hxk ), phosphofructokinase (pfk), or several enzymes of glycolysis (gcr). In diploids the mutations were recessive. pyk, pgi, pfk , and gcr segregated 2:2 from their wild-type alleles. PYK hxk, PYK pfk, and PYK gcr segregants grew on glucose.

https://www.genetics.org/content/genetics/88/1/1.full.pdf

Glycolysis mutants in Saccharomyces cerevisiae.

The glucose-dependent inactivation of malate dehydrogenase (l-malate: NAD oxidoreductase, EC 1.1.1.37) in acetate-grown yeast cells was studied in vivo. Among different yeast species inactivation was observed only in strains of the genus Saccharomyces. The phenomenon is initiated by the addition of glucose or related hexoses to the medium and is reversibly interrupted at 0°. By use of a yeast mutant requiring tryptophan, it was shown that malate dehydrogenase inactivation is not influenced by inhibition of protein synthesis, whereas recovery of enzyme activity in inactivated cells requires the presence of an energy source and tryptophan and is presumably due to de novo protein synthesis. The reported results provide evidence that a metabolite formed in the first steps of glycolysis might be responsible for initiation of malate dehydrogenase inactivation.

https://febs.onlinelibrary.wiley.com/doi/pdf/10.1111/j.1432-1033.1968.tb19533.x

W. Duntze

Papers

Glucose induced inactivation of malate dehydrogenase in intact yeast cells.