Freezing in yeast cells

Abstract

1. 1. A model is formulated which allows a calculation to be made from calorimetric data of the fraction of the yeast cell that is frozen as a function of sub-freezing temperatures. This model is independent of the position of the frozen water, whether intracellular of extracellular. 2. 2. Our normal yeast cell contains 69% total water. As the temperature is lowered below 0° C a progressive amount of this is frozen unti at − 22° approximately 87% of this total water is frozen. In the region from −22° to −72° the total frozen decreases to 74%. These calculations are based on the assumption that the specific heat of the non-freezable water (bound water) is the same as that of normal water. 3. 3. It is possible to adjust the computed curve so that the frozen fraction of cellular water does not decrease with temperature below −22° C by the assumption that the specific heat of the bound water component is not 1. With this assumption, the fraction of the cellular water that is frozen over the range from −22° to −72° is 0.91. Thus 9% of the total water is considered bound. The specific heat of bound water that emerges from these calculations is 0.26 ± 0.18 cal/gram C°. 4. 4. Data on the survival of yeast under these freezing conditions show that cells can survive even though as much as 90% of their cellular water is frozen. 5. 5. Certain radiobiological data indicate that at least a portion of this frozen water is located within the cell.