Regulation of the tricarboxylic acid cycle and poly-beta-hydroxybutyrate metabolism in Azotobacter beijerinckii grown under nitrogen or oxygen limitation.
Azotobacter beijerinckii was grown in ammonia-free glucose/mineral salts media in chemostat culture under oxygen or nitrogen limitation. Selected enzymes of the tricarboxylic acid cycle and poly-beta-hydroxybutyrate metabolism were monitored in relation to oxygen supply for both steady and transition states. Two dissolved oxygen concentrations were used for the nitrogen-limited steady state to investigate the possible effects of respiratory protection of nitrogenase on these enzymes. The levels of NADH oxidase, isocitrate dehydrogenase and 2-oxoglutarate dehydrogenase increased markedly on relaxation of oxygen limitation while pyruvate dehydrogenase and citrate synthase were relatively unaffected. beta-Ketothiolase and acetoacetyl-CoA reductase levels decreased as oxygen limitation was relaxed. Respiratory activity, as measured by the QO2 value, increased with oxygen supply rate. Imposition of oxygen limitation on a nitrogen-limited culture caused an immediate increase in the NADH/NAD ratio but this rapidly readjusted to its previous steady-state value. These changes are discussed in relation to respiratory protection of nitrogenase and poly-beta-hydroxybutyrate metabolism in A. beijerinckii.
D000101:Acetyl-CoA C-Acetyltransferase / Q000378:metabolism; D000429:Alcohol Oxidoreductases / Q000378:metabolism; D001395:Azotobacter / Q000201:enzymology / Q000378:metabolism*; D002950:Citrate (si)-Synthase / Q000378:metabolism; D002952:Citric Acid Cycle; D006885:Hydroxybutyrates / Q000378:metabolism*; D007521:Isocitrate Dehydrogenase / Q000378:metabolism; D007655:Ketoglutarate Dehydrogenase Complex / Q000378:metabolism; D009243:NAD / Q000378:metabolism; D009247:NADH, NADPH Oxidoreductases / Q000378:metabolism; D009584:Nitrogen / Q000378:metabolism*; D010101:Oxygen Consumption; D011768:Pyruvate Dehydrogenase Complex / Q000378:metabolism
D006885:Hydroxybutyrates; D011768:Pyruvate Dehydrogenase Complex; D009243:NAD; D000429:Alcohol Oxidoreductases; D007521:Isocitrate Dehydrogenase; D007655:Ketoglutarate Dehydrogenase Complex; D009247:NADH, NADPH Oxidoreductases; D000101:Acetyl-CoA C-Acetyltransferase; D002950:Citrate (si)-Synthase; D009584:Nitrogen