Sugar Retention, Cofactor Levels, and Leakage of Metabolites in X-Irradiated, Starved Yeast Cells

Measurements to clarify the factors responsible for a higher rate of CO₂ production by X-irradiated starved yeast cells than by unirradiated cells gave the following results: (1) In sugar transport experiments, irradiated cells retained a greater portion of|$\text{sorbose-}{}^{14}{\rm C}$|, though rates of efflux were similar during a first phase of exit and rates of uptake were similar. (2) Irradiated cells contained more thiamine pyrophosphate than unirradiated cells, whereas pyruvate decarboxylase activities and|${\rm ATP}^{2}$| and DPN contents were similar. (3) Similar amounts of 260-mμ-absorbing materials were lost by irradiated and unirradiated cells during starvation; incubation with glucose or maltose increased the total loss, while incubation with less readily metabolized sugars increased the relative loss from irradiated cells. (4) Higher doses of radiation did not greatly affect cell membrane stability as measured by turbidimetric changes in cells suspended in sugar solution. It is concluded that differences in transport capacity and permeability are not primarily involved in the difference in capacity to produce CO₂, but that the thiamine pyrophosphate content and the capacity of the cells to bind or compartment sugar appear to be directly related and are directly or indirectly affected by X-irradiation.