Biosynthesis of vitamin B12: factor IV, a new intermediate in the anaerobic pathway.

The structure of a novel tetradehydrocorrin, factor IV, isolated from Propionibacterium shermanii has been established by multidimensional NMR spectroscopy. Incorporation of radiolabeled factor IV into cobyrinic acid established the biointermediacy of this cobalt complex, whose structure has implications for the mechanisms of the anaerobic pathway to B12.

[Studies on the biological function of the nucleotide base of vitamin B12]. / Untersuchungen zur biologischen Funktion der Nucleotidbase von Vitamin B12.

Studies on the coenzyme activity of some nucleotide base analogues of adenosylcobalamine in the dioldehydratase and methyl-malonyl-CoA mutase systems resulted in fundamental differences: Contrary to dioldehydratase the coenzyme activity remains in the methyl-malonyl-CoA mutase system when adenosyl-cobamides with a strongly modified nucleotide base are studied. The analogues give a good growth response with Escherichia coli. In the growth test with Lactobacillus leichmanii only the cobamides that do not have substituted nucleotide bases in the positions 2 or 3 of their imidazole ring are active.

[Deamination and reductive deamination of (2-amino-5, 6-dimethylbenzimidazolyl)cobamide. Preparation of (2-hydroxy-5, 6-dimethylbenzimidazolyl)cobamide and (5, 6-dimethyl-[2(-14)C]-benzimidazolyl)cobamide]. / Desaminierung und reduktive Desaminierung von (2-Amino-5, 6-dimethylbenzimidazolyl)cobamid. Darstellung von (2-Hydroxy-5 6-dimethylbenzimidazolyl)cobamid und (5, 6-Dimethyl-[2(-14)C] benzimidazolyl)cobamid.

(2-Amino-5, 6-dimethylbenzimidazolyl)-cobamide (III) is transformed to (2-hydroxy-5, 6-dimethylbenzimidazolyl) cobamide (IV) by nitrous acid. Exchange of the NH2-group by hydrogen with nitrous acid/hypophosphorous acid yields vitamin B12 (I). This reaction completes a cycle vitamin B12 (I)----[carboxy(2-cyanoamino-4,5-dimethylphenyl)amino]cobamide+ ++ (II)----(2-amino-5,6-dimethylbenzimidazolyl)cobamide (III)----vitamin B12 (I), which allows chemical 14C-labelling of vitamin B12. In this procedure cyanogen bromide, which is necessary for the first step, was labelled with [14C] cyanide. By the following reactions a vitamin B12 was formed in which C-2 of the 5, 6-dimethylbenzimidazole moiety is labelled.