The route of ethanol formation in Zymomonas mobilis

Abstract

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