title: Poly- -hydroxybutyrate biosynthesis and the regulation of glucose metabolism in Azotobacter beijerinckii.
abstract: Azotobacter beijerinckii possesses the enzymes of both the Entner-Doudoroff and the oxidative pentose phosphate cycle pathways of glucose catabolism and both pathways are subject to feedback inhibition by products of glucose oxidation. The allosteric glucose 6-phosphate dehydrogenase utilizes both NADP(+) and NAD(+) as electron acceptors and is inhibited by ATP, ADP, NADH and NADPH. 6-Phosphogluconate dehydrogenase (NADP-specific) is unaffected by adenosine nucleotides but is strongly inhibited by NADH and NADPH. The formation of pyruvate and glyceraldehyde 3-phosphate from 6-phosphogluconate by the action of the Entner-Doudoroff enzymes is inhibited by ATP, citrate, isocitrate and cis-aconitate. Glyceraldehyde 3-phosphate dehydrogenase is unaffected by adenosine and nicotinamide nucleotides but the enzyme is non-specific with respect to NADP and NAD. Citrate synthase is strongly inhibited by NADH and the inhibition is reversed by the addition of AMP. Isocitrate dehydrogenase, a highly active NADP-specific enzyme, is inhibited by NADPH, NADH, ATP and by high concentrations of NADP(+). These findings are discussed in relation to the massive synthesis of poly-beta-hydroxybutyrate that occurs under certain nutritional conditions. We propose that synthesis of this reserve material, to the extent of 70% of the dry weight of the organism, serves as an electron and carbon ;sink' when conditions prevail that would otherwise inhibit nitrogen fixation and growth.
mesh_terms: D031841:Aconitum / Q000494:pharmacology; D000244:Adenosine Diphosphate / Q000494:pharmacology; D000255:Adenosine Triphosphate / Q000494:pharmacology; D001395:Azotobacter / Q000378:metabolism*; D002951:Citrates / Q000494:pharmacology; D005947:Glucose / Q000378:metabolism*; D005987:Glyceraldehyde-3-Phosphate Dehydrogenases / Q000037:antagonists & inhibitors; D006885:Hydroxybutyrates / Q000096:biosynthesis*; D007523:Isocitrates / Q000494:pharmacology; D009243:NAD / Q000494:pharmacology; D009249:NADP / Q000494:pharmacology; D009586:Nitrogen Fixation; D010084:Oxidation-Reduction; D010085:Oxidative Phosphorylation; D010734:Phosphogluconate Dehydrogenase / Q000037:antagonists & inhibitors; D011773:Pyruvates / Q000096:biosynthesis
chemical_list: D002951:Citrates; D006885:Hydroxybutyrates; D007523:Isocitrates; D011773:Pyruvates; D009243:NAD; D009249:NADP; D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate; D010734:Phosphogluconate Dehydrogenase; D005987:Glyceraldehyde-3-Phosphate Dehydrogenases; D005947:Glucose