n(1)-(5-phosphoribosyl)-5-6-dimethylbenzimidazole and alpha-ribazole

The genomes of Listeria spp. encode all but one of 25 enzymes required for the biosynthesis of adenosylcobalamin (AdoCbl; coenzyme B(12) ). Notably, all Listeria genomes lack CobT, the nicotinamide mononucleotide:5,6-dimethylbenzimidazole (DMB) phosphoribosyltransferase (EC 2.4.2.21) enzyme that synthesizes the unique α-linked nucleotide N(1) -(5-phospho-α-D-ribosyl)-DMB (α-ribazole-5'-P, α-RP), a precursor of AdoCbl. We have uncovered a new pathway for the synthesis of α-RP in Listeria innocua that circumvents the lack of CobT. The cblT and cblS genes (locus tags lin1153 and lin1110) of L. innocua encode an α-ribazole (α-R) transporter and an α-R kinase respectively. Results from in vivo experiments indicate that L. innocua depends on CblT and CblS activities to salvage exogenous α-R, allowing conversion of the incomplete corrinoid cobinamide (Cbi) into AdoCbl. Expression of the L. innocua cblT and cblS genes restored AdoCbl synthesis from Cbi and α-R in a Salmonella enterica cobT strain. LinCblT transported α-R across the cell membrane, but not α-RP or DMB. UV-visible spectroscopy and mass spectrometry data identified α-RP as the product of the ATP-dependent α-R kinase activity of LinCblS. Bioinformatics analyses suggest that α-R salvaging occurs in important Gram-positive human pathogens.

Topics: Bacterial Proteins; Benzimidazoles; Cloning, Molecular; Cobamides; Computational Biology; DNA, Bacterial; Listeria; Multienzyme Complexes; Nucleotidyltransferases; Pentosyltransferases; Phosphorylation; Plasmids; Protein Kinases; Ribonucleosides; Ribonucleotides; Salmonella enterica

A method to determine the contents of free vitamin B12 in various foods by reversed phase liquid chromatography-fluorimetry is reported. It includes a purification of the samples by passage through an immunoaffinity column and a pre-column conversion of vitamin B12 into the fluorescent alpha-ribazole (successive treatments of the extract with 2.5 M sodium hydroxide (at 100 degrees C for 15 min) and alkaline phosphatase (7.5 U) at 37 degrees C and pH 8 for 16 h). An enzymatic hydrolysis prior to the purification step (pepsin at 37 degrees C and pH 4 for 3 h) made it possible to release the vitamin B12 bound to proteins and thus to obtain the total vitamin B12 contents of these foodstuffs. The method proposed for the determination of free and bound vitamin B12 gives a good recovery rate (95-100%) and a satisfactory repeatability (R.S.D.r between 1.0 and 5.4%). Owing to its low quantification limit (3 ng g(-1)) and the good resolution of the alpha-ribazole peak, it could most probably be applied to the determination of this vitamin in any foodstuff.

Topics: Alkaline Phosphatase; Benzimidazoles; Chromatography, High Pressure Liquid; Fluorescent Dyes; Fluorometry; Food Analysis; Ribonucleosides; Ribonucleotides; Vitamin B 12