Morphological and biochemical effects of freezing on yeast cells

1. 1. Some changes in the structure and metabolism of yeast cells which occur on freezing with solid CO2 are described. 2. 2. CO2-frozen cells, besides being permeable to addrd organic acids, lose organic acids, amino acids, protein, carbohydrate, coenzymes and inorganic salts when washed with water or buffer. 3. 3. The ability of such cells to respire ethanol and succinate may not be a reliable guide to the normal metabolism of these substrates, since the response to varying degrees of temperature-shock differs according to the strain of bakers' yeast used. 4. 4. Freezing reduces the amount of sedimentable material in cell-free extracts prepared by ultra-rapid shaking. In this respect, the effects of freezing resemble those obtained by disintegrating fresh cells for longer periods. Partial solubilization of granular fumarase, aconitase, and ethanol and malic dehydrogenases occurs, and aconitase is partially inactivated. 5. 5. The coenzyme-independent ethanol and malic dehydrogenase activities found in extracts of fresh yeast are lacking in extracts of frozen yeast. The possibility of coenzyme-binding, the disruptive action of thermal shock and the evidence for the participation of the tricarboxylic acid cycle in acetate oxidation by bakers' yeast, are discussed.