corrin and 5-6-dimethylbenzimidazole

Corrinoid (vitamin B12-like) cofactors contain various alpha-axial ligands, including 5,6-dimethylbenzimidazole (DMB) or adenine. The bacterium Salmonella enterica produces the corrin ring only under anaerobic conditions, but it can form "complete" corrinoids aerobically by importing an "incomplete" corrinoid, such as cobinamide (Cbi), and adding appropriate alpha- and beta-axial ligands. Under aerobic conditions, S. enterica performs the corrinoid-dependent degradation of ethanolamine if given vitamin B12, but it can make B12 from exogenous Cbi only if DMB is also provided. Mutants isolated for their ability to degrade ethanolamine without added DMB converted Cbi to pseudo-B12 cofactors (having adenine as an alpha-axial ligand). The mutations cause an increase in the level of free adenine and install adenine (instead of DMB) as an alpha-ligand. When DMB is provided to these mutants, synthesis of pseudo-B12 cofactors ceases and B12 cofactors are produced, suggesting that DMB regulates production or incorporation of free adenine as an alpha-ligand. Wild-type cells make pseudo-B12 cofactors during aerobic growth on propanediol plus Cbi and can use pseudo-vitamin B12 for all of their corrinoid-dependent enzymes. Synthesis of coenzyme pseudo-B12 cofactors requires the same enzymes (CobT, CobU, CobS, and CobC) that install DMB in the formation of coenzyme B12. Models are described for the mechanism and control of alpha-axial ligand installation.

Topics: Adenine; Adenine Phosphoribosyltransferase; Aerobiosis; Anaerobiosis; Bacterial Proteins; Benzimidazoles; Chromatography, High Pressure Liquid; Cobamides; Corrinoids; Ethanolamine; Gene Expression Regulation, Bacterial; Ligands; Mass Spectrometry; Models, Biological; Molecular Structure; Mutagenesis; Mutation; N-Glycosyl Hydrolases; Phenotype; Polymerase Chain Reaction; Salmonella enterica; Vitamin B 12

Burgus, R. C. (Wayne State University, Detroit, Mich.), J. B. Hufham, W. M. Scott, and J. J. Pfiffner. Microbial degradation of corrinoids. III. Pigments derived from vitamin B(12) by Pseudomonas rubescens. J. Bacteriol. 88:1139-1144. 1964.-Products derived from vitamin B(12) by Pseudomonas rubescens under anaerobic conditions were examined. After incubation of the organism in broth containing Co(57)- or P(32)- vitamin B(12), electrophoresis of the extracted corrinoids yielded two major, yellow, radioactive fractions, designated A and B, with spectral and electrophoretic properties similar to pigments I and II, derived from vitamin B(12) by Aerobacter aerogenes. Fractions A and B were essentially inactive in promoting the growth of Lactobacillus leichmannii. Chromatography on carboxymethylcellulose separated both fractions A and B into four yellow, radioactive fractions. The absorption spectrum of each of the major subfractions showed a maximum in the ultraviolet region characteristic of a 5,6-dimethylbenzimidazole nucleotide, but lacked a maximum in the 360-mmu region characteristic of vitamin B(12) and many of its analogues and derivatives. The pigments were stable to cyanide and, although they were more stable to air and light than were the vitamin B(12) coenzymes and coenzyme analogues, they were apparently slowly decomposed by light. The data suggest that the bacteria alter the corrin nucleus of vitamin B(12).

Topics: Benzimidazoles; Chemical Phenomena; Chemistry; Chromatography; Coenzymes; Corrinoids; Cyanides; Electrophoresis; Enterobacter aerogenes; Lactobacillus; Metabolism; Pigments, Biological; Pseudomonas; Research; Spectrum Analysis; Vitamin B 12