Affiliation:
1. Department of Biology, Sinsheimer Laboratories, University of California, Santa Cruz 95064.
Abstract
A complete pathway for Azorhizobium caulinodans nicotinate catabolism has been determined from mutant phenotype analyses, isolation of metabolic intermediates, and structural studies. Nicotinate serves as a respiratory electron donor to O2 via a membrane-bound hydroxylase and a specific c-type cytochrome oxidase. The resulting oxidized product, 6-hydroxynicotinate, is next reduced to 1,4,5,6-tetrahydro-6-oxonicotinate. Hydrolytic ring breakage follows, with release of pyridine N as ammonium. Decarboxylation then releases the nicotinate C-7 carboxyl group as CO2, and the remaining C skeleton is then oxidized to yield glutarate. Transthioesterification with succinyl coenzyme A (succinyl-CoA) yields glutaryl-CoA, which is then oxidatively decarboxylated to yield crotonyl-CoA. As with general acyl beta oxidation, L-beta-hydroxybutyryl-CoA, acetoacetyl-CoA, and finally two molecules of acetyl-CoA are produced. In sum, nicotinate is catabolized to yield two CO2 molecules, two acetyl-CoA molecules, and ammonium. Nicotinate catabolism stimulates Azorhizobium N2 fixation rates in culture. Nicotinate catabolism mutants still able to liberate pyridine N as ammonium retain this capability, whereas mutants so blocked do not. From, mutant analyses and additional physiological tests, N2 fixation stimulation is indirect. In N-limited culture, nicotinate catabolism augments anabolic N pools and, as a consequence, yields N2-fixing cells with higher dinitrogenase content.
Publisher
American Society for Microbiology
Subject
Molecular Biology,Microbiology
Reference28 articles.
1. Ausubel F. M. R. Brent R. E. Kingston D. D. Moore J. A. Smith J. G. Seidman and K. Struhl (ed.). 1987. Current protocols in molecular biology. John Wiley & Sons Inc. New York.
2. The bacterial oxidation of nicotinic acid;Behrman E. J.;J. Biol. Chem.,1957
3. Effects of 02 concentrations and various haemoglobins on respiration and nitrogenase activity of bacteroids from the stem and root nodules of Sesbania rostrata and of the same bacteria from continuous cultures;Bergersen F. J.;J. Gen. Microbiol.,1986
4. Cloning of the Azorhizobium caulinodans nicotinate catabolism genes and characterization of their importance in N2 fixation;Buckmiller L. M.;J. Bacteriol.,1991
5. Characterization of the Azorhizobium sesbaniae ORS571 genomic locus encoding NADPH-glutamate synthase;Donald R. G. K.;J. Bacteriol.,1988
Cited by
24 articles.
订阅此论文施引文献
订阅此论文施引文献,注册后可以免费订阅5篇论文的施引文献,订阅后可以查看论文全部施引文献