Variations of two pools of glycogen and carbohydrate in Saccharomyces cerevisiae grown with various ethanol concentrations.

Glycogen, a major reservoir of energy in Saccharomyces cerevisiae, is found to be present as soluble and membrane-bound insoluble pools. Yeast cells can store excess glycogen when grown in media with higher concentration of sugar or when subjected to nutritional stress conditions. Saccharomyces cerevisiae NCIM-3300 was grown in media having ethanol concentrations up to 12% (v/v). The effects of externally added ethanol on glycogen and other carbohydrate content of yeast were studied by using alkali digestion process. Fermentative activities of cells grown in the presence of various ethanol concentrations (2-8% v/v) exhibited increase in values of glycogen and other carbohydrate, whereas cells grown with higher concentrations of ethanol (10-12% v/v) exhibited depletion in glycogen and carbohydrate content along with decrease in cell weight. Such inhibitory effect of ethanol was also exhibited in terms of reduction in total cell count of yeast grown in media with 2-16% (v/v) ethanol and 8% (w/v) sugar. These data suggest that, as the plasma membrane is a prime target for ethanol action, membrane-bound insoluble glycogen might play a protective role in combating ethanol stress. Elevated level of cell-surface alpha-glucans in yeast grown with ethanol, as measured by using amyloglucosidase treatment, confirms the correlation between ethanol and glycogen.

Beta-amylase-resistant amylose. Effect of urea on the limited hydrolysis of amylose by beta-amylase.

Amylose prepared from starch dispersed in 10M-urea, pH6.2, was found to be resistant to the action of beta-amylase and phosphorylase, though it was degraded by alpha-amylase. Amylose isolated by conventional methods was similarly refractory after urea treatment, and was hydrolysed by beta-amylase to the extent of 32-35%; it had no inhibitory effect towards beta-amylase. The physical and chemical properties of the modified amylose were in general comparable with those of normal amylose with a beta-amylolysis limit of 94-98%. Starch and amylopectin were unaffected by urea treatment, i.e. the presence of amylopectin protected amylose against changes induced in it by urea. It is speculated that urea treatment "freezes" amylose molecules in a conformation that renders non-reducing termini inaccessible to the active site of the exo-enzymes. Such changes may limit the degradative action of beta-amylase and phosphorylase.

Two pools of glycogen in Saccharomyces.

The effect of different extraction procedures on the yields of water-soluble and water-insoluble glycogen fractions from a number of Saccharomyces strains was studied by using a specific method for glycogen determination. The similarity of the yields obtained by the different procedures showed that neither form of glycogen is an artifact, and variations in the relative amounts of glycogen in the two fractions during cell growth and in different yeast strains suggest that they represent different pools of storage material with specific roles in cell development and differentiation. A proportion of the water-insoluble glycogen fraction, solubilized by mechanical agitation, was shown to be strongly associated with a beta-glucan-like polysaccharide that may be a cell wall component.