Further Observations on Carbohydrate Metabolism and its Regulation in Azotobacter beijerinckii

Abstract

Certain enzymes of glucose catabolism in A. beijerinckii were studied and their activities in steady-state chemostat cultures were measured under various nutrient limitations. 2-Keto-3-deoxy-6-phosphogluconate aldolase was separated from 6-phosphogluconate dehydratase by affinity chromatography and the previously observed inhibition of the Entner-Doudoroff enzymes by tricarboxylic acids and ATP was attributed to chelation of Mn2+ and Mg2+ which activate the dehydratase. Glucose-6-phosphate dehydrogenase was unaffected by phosphoenolpyruvate while fructose-1,6-bisphosphate aldolase was activated by Co2+, K+ or NH4+ ions. Transketolase, transaldolase and triosephosphate isomerase were present but previous reports of 6-phosphogluconate dehydrogenase activity were shown to be artefacts. The findings confirm the major role of the Entner-Doudoroff pathway in glucose catabolism in A. beijerinckii. Pyruvate dehydrogenase, a key enzyme for C entry to tricarboxylic acid cycle and to poly-.beta.-hydroxybutyrate synthesis, was inhibited by acetyl-coenzyme A and NADH.