A cell-wall-surface protein purified from the cells of Saccharomyces cerevisiae NCYC 227 was found to be involved in the non-sexual flocculation of this yeast. This 13 kDa protein was found to bind specifically to mannose. The protein bound to mannans isolated from yeast as well as in situ to intact cells, but only in the presence of calcium ions. The protein, a mannoprotein, formed aggregates as revealed in SDS-PAGE. Urea and higher temperatures prevented protein aggregation, suggesting that the flocculation of S. cerevisiae is primarily due to hydrogen bonding between mannan and protein.
In rapidly fermenting yeast, the rotenone insensitive mitochondrial NADH dehydrogenase was not completely repressed by high glucose. This activity appeared to enhance the glycolytic rate due to which acetaldehyde accumulated intracellularly. To overcome the toxicity of acetaldehyde, the strain produced stress proteins. During late stationary phase of growth, the accumulated acetaldehyde was converted to ethanol resulting in faster ethanol production.
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