Respiration and viability of thermally injured Saccharomyces cerevisiae.

Resting cells of Saccharomyces cerevisiae Y25 were heated at 56 degrees C for 0 to 2 min. Respiratory activity of the cells reflected the severity of the heat stress. The endogenous respiration was approximately 50 microliter of O2/mg per h for cells heated for 2 min at 56 degrees C as compared with 2 microliter of O2/mg per h for nonheated cells. There was a distinct decrease in respiration after 1 to 3 h, and after 20 h the respiration rate of heated cells was less than that of nonheated cells. Along with increased rates of endogenous respiration, respiratory quotients of cells were altered after heat stress. Addition of 2,4-dinitrophenol stimulated O2 (uptake) in nonheated cells but decreased O2 (uptake) of heated cells. Due to the high rate of endogenous respiration, addition of glucose resulted in no substantial change in the rate of respiration of heated cells. However, addition of glucose prolonged the presence of the high rates of respiration observed in heated cells.