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Fermentation of glucose by resting cells and cell-free extracts of the obligate psychrophile Candida gelida was essentially abolished after being heated for 30 minutes at 35 C. A survey of the enzymes of the yeast alcoholic fermentation pathway revealed that pyruvate decarboxylase was the only temperature-sensitive enzyme. Kinetic studies of thermal inactivation showed that C. gelida pyruvate decarboxylase was 50% inactivated after it was heated for 10 minutes at 35 C. Restoration of glucose fermentation rate in heated extracts from C. gelida, after addition of purified yeast pyruvate decarboxylase, confirmed that heat-induced loss of fermentative activity was due to inactivation of a temperature-sensitive pyruvate decarboxylase.

1. Enzymic evidence supporting the operation of the Entner–Doudoroff pathway in the anaerobic conversion of glucose into ethanol and carbon dioxide by Zymomonas mobilis is presented. 2. Cell extracts catalysed the formation of equimolar amounts of pyruvate and glyceraldehyde 3-phosphate from 6-phosphogluconate. Evidence that 3-deoxy-2-oxo-6-phosphogluconate is an intermediate in this conversion was obtained. 3. Cell extracts of the organism contained the following enzymes: glucose 6-phosphate dehydrogenase (active with NAD and NADP), ethanol dehydrogenase (active with NAD), glyceraldehyde 3-phosphate dehydrogenase (active with NAD), hexokinase, gluconokinase, glucose dehydrogenase and pyruvate decarboxylase. Extracts also catalysed the overall conversion of glycerate 3-phosphate into pyruvate in the presence of ADP. 4. Gluconate dehydrogenase, fructose 1,6-diphosphate aldolase and NAD–NADP transhydrogenase were not detected. 5. It is suggested that NAD is the physiological electron carrier in the balanced oxidation–reduction involved in ethanol formation.