Calorimetric study on the sugar metabolism of yeast under nongrowing conditions.

Abstract

When glucose was added to a washed suspension of yeast under aerobic conditions, the heat production curve showed three distinct phases which reflect the metabolic process. The first phase showed a sharp peak which may be attributed to the uptake of glucose the rate of which was proportional to the cell concentration. The results of chemical analyses suggest that the second phase is connected to the metabolism of ethanol, which is followed by the third phase of endogenous metabolism. The second and third phases were nearly absent under anaerobic conditions or when respiration was inhibited. The amount of cellular trehalose, which serves as an energy source, was reflected by the physiological state of the cells, but showed little effect on heat production. The heat produced was proportional to the glucose concentration, depending on the temperature. There were some differences between glucose metabolism and endogenous metabolism in the temperature effect on the rate of heat production. Some correlations between heat production and ATP were observed under anaerobic conditions, but no correlation was observed under aerobic conditions. A comparison was made of enthalpy change with different types of metabolism of yeast. The calorimetric measurements are considered to be a useful approach in studying sugar uptake processes.