The control of glycogen metabolism in yeast. 1. Interconversion in vivo of glycogen synthase and glycogen phosphorylase induced by glucose, a nitrogen source or uncouplers (original) (raw)
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Biochimica Et Biophysica Acta General Subjects, 1980
Glucose can block the utilization of N-acetylglucosamine in Saccharomyces cerevisiae, a facultative aerobe, but not in Candida albicans, an obligatory aerobe. Furthermore, glucose represses the synthesis of the enzymes of the N-acetylglucosamine catabolic pathway in S. cerevisiae, but not in C. albicans. The results suggest that catabolite repression is present in S. cerevisiae, but not in C. albicans. Cyclic AMP added to S. cerevisiae cells maintained in a glucose medium cannot bring about their release from catabolite repression. On the contrary, the synthesis of inducible enzymes of N-acetylglucosamine pathway was inhibited by cyclic AMP in both the yeasts. This seems to indicate that cyclic AMP can penetrate into the yeast cells. Furthermore, cyclic AMP inhibits protein synthesis, suggesting that protein synthesis in yeast is under cyclic AMP control.
Proceedings of The National Academy of Sciences, 1993
The systems which control the levels of the gluconeogenic enzymes in Saccharomyces cerevisiae have been bypassed to ascertain their physiological significance. The coding regions of the genes FBP1 and PCK1, which encode fructose-1,6-bisphosphatase and phosphoenolpyruvate carboxykinase, have been put under the control of the promoter of ADC1 (alcohol dehydrogenase I), a gene not repressed by glucose, and introduced into yeast in multicopy plasmids. The transformed yeast cells show high levels of the gluconeogenic enzymes during growth on glucose. Generation time and growth yield of yeast expressing either fructose-1,6-bisphosphatase or phosphoenolpyruvate carboxykinase are not significantly different from those of the wild-type strain. For a strain expressing both enzymes the increase in generation time is about 20% and the decrease in growth yield around 30%. The concentration of ATP is about 1.5 mM in the growing cells of the different strains. The extent of in vivo cycling was measured by 13 C NMR in cell-free extracts from yeast growing on [6-13 C]glucose. Cycling between fructose-6-phosphate and fructose-1,6-bisphosphate is <2%, most likely due to the very strong inhibition of fructose-1,6-bisphosphatase by fructose 2,6-bisphosphate. Cycling between phosphoenolpyruvate and pyruvate is low, but a precise figure could not be obtained due to poor equilibration of label between carbons 2 and 3 of oxaloacetate.
Glycogen phosphorylase activity in permeabilized cells of Saccharomyces cerevisae
Biochimica et Biophysica Acta (BBA) - Enzymology, 1974
The velocity of formation of glucose 6-phosphate and glucose by protamine-treated permeabilized yeast cells was dependent on the concentration of inorganic phosphate. Fluoride inhibited the reaction. Only small amounts of glucose 6-phosphate were produced in presence of ATP and glucose. We conclude that we are measuring the glycogen phosphorylase reaction inside the permeabilized cells.
The Effect of the nature of the Substrate on the Rate of Cellular Respiration on yeast 1
The effect of the nature of the substrates on the rate of cellular respiration on yeast was measured using the Smith Fermentation tube method. Six smith fermentation tubes and five substrates were prepared: glucose, sucrose, fructose, lactose and starch. 15 ml of each substrate was put separately on each of the tubes and was labelled. 15 ml of distilled water was put separately on the tubes together with the sugars and another 15 ml of yeast suspension was put. The tubes were shook and were observed for 30 minutes. It was seen that the enzymes broke down the sugars into carbon dioxide as product. According to the experiment done, sucrose had the fastest rate of respiration obtaining a rate of 0.228 cm 3 /min, next is glucose having a rate of 0.219 cm 3 /min, then fructose having a rate of 0.189 cm 3 /min. The tube with the distilled water, starch and lactose had no volume of carbon dioxide, this means that no respiration occurred. Because a disaccharide, sucrose, had the fastest rate of respiration, next are the monosaccharides then lactose and starch, the hypothesis: If the nature of the substrate affects the rate of cellular respiration on yeast, then the simpler the substrate, the faster the rate of respiration, was rejected. This means that the nature of the substrate does not affect the cellular rate of respiration on yeast.
Glucose and sucrose: hazardous fast-food for industrial yeast
Trends in Biotechnology, 2004
Yeast cells often encounter a mixture of different carbohydrates in industrial processes. However, glucose and sucrose are always consumed first. The presence of these sugars causes repression of gluconeogenesis, the glyoxylate cycle, respiration and the uptake of lesspreferred carbohydrates. Glucose and sucrose also trigger unexpected, hormone-like effects, including the activation of cellular growth, the mobilization of storage compounds and the diminution of cellular stress resistance. In an industrial context, these effects lead to several yeast-related problems, such as slow or incomplete fermentation, 'off flavors' and poor maintenance of yeast vitality. Recent studies indicate that the use of mutants with altered responses to carbohydrates can significantly increase productivity. Alternatively, avoiding unnecessary exposure to glucose and sucrose could also improve the performance of industrial yeasts.
Effect of Variable Sugar Concentrations on Glycogen and Ethanol Content in Saccharomyces sp
International Journal of Food Engineering, 2011
Saccharomyces cerevisiae (MTCC-12) maintains two pools of glycogen, one soluble and the other cell wall bound insoluble glycogen. Effect of variable concentrations of sugar on the insoluble pool of glycogen linked to wall β-glucan component was found to be more significant than that observed for soluble pool of glycogen. The study revealed that cells exhibit exponential increase in the amount of insoluble glycogen with corresponding increase in sugar concentration from 2-10 % (w/v). Ethanol content as well as concentration of insoluble glycogen in yeast cells, which were grown in sucrose medium, shows higher values than in glucose medium. Parallel increase in glycogen and ethanol content indicates their correlation with each other. Exponential increase in insoluble glycogen content serves as a protective measure against ethanol stress created across the plasma membrane of yeast cell.
Novel Application of Glucagon and Insulin to Alter Yeast Glycogen Concentrations
Journal of The American Society of Brewing Chemists, 1995
The glycogen content of brewers' yeasts has been used as an indicator of yeast vitality. Methods to artificially manipulate the yeast glycogen content rely on steps that could be expected to alter other cellular components. Consequently, an evaluation of the performance of such cells may not be directly related to glycogen concentrations. To alter only the cellular glycogen contents, we investigated the use of the hormones glucagon and insulin. Three different physiological conditions of yeast (aerobically grown, brewery fresh, and aged) were used. We found that both insulin and glucagon functioned as expected from their known activity in higher eucaryotes (mammals). Insulin promoted the conversion of glucose into glycogen. Glucagon stimulated glycogen breakdown and inhibited its synthesis at the end of fermentation. The effects of glucagon and insulin on glycogen level were enhanced in brewery-fresh yeast compared to aerobically grown yeast but minimal in aged yeast. It was postulated that diffusive movement of insulin and glucagon into the cell was eased in the case of yeast that actively divided. Increased membrane permeability also facilitated entry. These hormones may prove to be very useful metabolic tools to alter cellular glycogen concentrations without causing non-specific effects on commonly measured fermentation parameters.
European journal of biochemistry / FEBS, 1987
Changes in the concentration of several metabolites and enzymes related to carbohydrate metabolism were measured during the growth of Saccharomyces cerevisiae on a mineral medium containing glucose as the limiting nutrient. When about 50% of the original glucose was used the exponential phase ended and the culture entered a 'transition' phase before the complete exhaustion of glucose. In this transition phase several metabolic changes occurred. cAMP, that decreased along growth, reached a constant value of about 0.7 nmol/g dry weight. A pronounced drop in fructose-6-phosphate-2-kinase activity and in the concentration of fructose 2,6-bisphosphate and fructose 1,6-bisphosphate was observed accompanied by a less marked decrease in hexose monophosphates. Trehalase activity also dropped and reached a minimal value at the onset of the stationary phase when synthesis of trehalose began. Glycogen concentration and glycogen synthase activity increased sharply during the transition p...
Biosystems, 1982
To localise the controlling point of the glycolytic system, the temporal changes of concentrations of glycolytic intermediates have been analysed after addition of glycogen to a substrate-depleted yeast extract. Three sequential metabolic slates are clearly observable: a transition state at which there is continuous accumulation of the intermediates befol:e the glyceraldehydephosphate dehydrogenase (GAPDH, EC 1.2.1.12)step; a stationary state with all glycolytic intermediates having concentrations oscillating at nearly stationary mean values; and a depletion state at which the intermediates before the GAPDH step are being depleted due to the exhaustion of glycogen. In all these states, the mean ethanol production rate and the concentration of ATP and the intermediates beyond the GAPDH-step are maintained fairly constant, while the glycogen consumption rate and intermediate concentrations of the upper part of the glycolytic system change considerably: the glycogen consumption rate varies 4-fold and fructose-bis-phosphate concentration more than 10-fold. Doubling of the initial glycogen concentration and the addition of a great excess of fructose-bis-pbosphate do not affect the ethanol production rate and the mean glycerate-3-phosphate (3-PGA) and pyruvate levels. By contrast, ethanol production was accelerated by an increase of the net ATP consumption rate resulting from either the addition of apyrase or by substitution of trehalose for glycogen. Neither the mean absolute ATP level nor the adenylate energy charge were measurably affected, however all this data can be interpreted in terms of a very strong stoichiometric regulation and stabilization of the lower part of the glycolytic system.