Vitamin Cobamide

Microbiological assay should stress accuracy over precision. Standardization of an assay method should include comparisons with at least one other organism having a different nutritional pattern and specificity toward the compound being assayed. Such a comparison was made for cyanocobalamin (vitamin Bi2 ) content of human blood and serum, using four microorganisms differing in their cobamide requirements and metabolism (B9). 

Vitamin Bj2 (cyanocobalamine, a-[5,6-dimethylbenzimidazolyl]cyano cobamide) [68-19-9] M 1355.4, dark at 210-220° and does not melt below 300°, [a] g 6 -59° (H2O). Crystd from de-ionized H2O, solubility in H2O is lg/80g and dried under vacuum over MgfClO. The dry red crystals are hygroscopic and can absorb -12% of H2O. A soln at pH 4.5-5 can be autoclaved for 20min at 120° without dec. Aqueous solns are stabilised by addition of (NH SO [Golding Comprehensive Organic Chem vol 5 (ed Haslam Pergamon Press, NY, 1979) pp549-584]. 

In view of work by Barker et al. (1960A,B) and Weissbach et al. (1961), it appears that the natural cobamide produced in bacterial cultures is not vitamin Bi2 but rather coenzyme B12. Berry and Bullerman (1966) and Bullerman and Berry (1966A.B) described a two-stage proc-... 

The catalysis of the transfer of a methyl group is an important role of enzyme-bound vitamin B12 derivatives in human, animal, and bacterial metabolism. The known enzyme-controlled methyl group-transfer reactions are key steps in the cobamide-dependent methylations of homocysteine to methionine, in the metabolic formation of methane from other Ci-compounds in methanogenic bacteria, and in the fixation of carbon dioxide via the acetyl coenzyme A pathway of some bacterial autotrophs (Figure 10). ... 

Coenzyme B12 Cobamide Hydrogen atoms and alkyl groups Vitamin B12... 

In the biosynthesis of the coenzymes derived from vitamin B 2. cobalt is reduced from a trivalent to a monovalent state before the organic anionic ligands are attached to the suuctuie. The two types of cobamide that participate as coenzymes in human metabolism are the adcnosylcobamides and the nKthylcobamides. These coenzymes perform vital functions in methylinalonate-succinate isomerization and in methylation of homocy.steine to methionine. 

The skeleton of vitamin 8,2 (i.e., the porphyrin nucleus minus C-20) is called corrin. The compound containing the corrin nucleus is edled a corrinoid. The compound containing the cobalt atom and the standard side chains in the free acid form is called cobyrinic acid, but cobyric acid when the side chains are at positions a, b, c, d, e, g, are in the amide form. Cobyrinic acid substituted with D-l-amino-2-propanol at position f is called cobinic acid. The substituted cobyric acid is called cobinamide. Cobinic acid substituted with d ribofuranose-3-phosphate at position 2 of the aminopropanol is called cobamic acid the substituted cobinamide is called cobamide. Many 8,2 vitamins and derivatives in which the heterocyclic base is 5,6-dimethylbenzimidazole are given the trivial name cobalamin see D. Dolphin, ed., 8,2, Wiley-Interscience, New York, 1982. 

Vitamin Bo (1, CNCbl), and other Bo-derivatives, where the cyanide ligand of 1 is replaced by a different upper /3-ligand are 5, 6 -dimethylbenzi-midazolyl-cobamides and are the most commonly discussed Bo-derivatives. Only base-on cobalamins, where the nucleotide functionality coordinates in an intramolecular mode, have been analyzed by x-ray crystallography [27, 28]. In this present chapter a systematic atomic numbering is used for vitamin... 

Cell fractionation studies of homogenates of the gastric mucosa have demonstrated that the intrinsic factor is found both in mitochondria and the supernatant fluid. The factor remains difficult to assay a variety of methods have been used, but none is entirely satisfactory. These methods include (1) administration of intrinsic factor preparation to gastrectomized animals (rats or hogs) (2) measurement of vitamin 6 2 binding capacity of the preparation (3) measurement of vitamin Bi2 uptake in tissue and (4) evaluation of the inhibition of cobamide coenzyme activity in the glutamate isomerase reaction. 

The structure of vitamin B12 was estabhshed as -(5,6-dimethylbenzimid-azolyl)cobamide cyanide (I) by chemical degradation and physical methods, particularly including X-ray crystallography. Details of these structural studies may be found in several reviews - . 

P. arabinosum and the bacteria that live in the gut of humans and animals synthesize mostly the purine-containing cobamides. If DMB is added to the feed, then the synthesis of cobalamins in the stomach of animals increases (Rickard et al., 1975). The finding of incomplete corrinoids in various bacteria and algae (Neujahr and Frires, 1966) shows that their biosynthesis may proceed with difficulty. Cobinamide, pseudo-vitamin B, factor A and factor III can act as growth factors for microorganisms if they contain a nucleotide, they are also active in enzymatic reactions in animals. 

Freer J, Kim KS, Krauss MR, Beaman L and Barksdale L (1969) Ultrastmctural changes in bacteria isolated from cases of leprosy. J Bacteriol 100 1062-1075 Frey B, McCloskey J, Kersten W and Kersten H (1988) New function of vitamin B12 cobamide-dependent reduction of epoxyquenosine to quenosine in tRNAs of Escherichia coli and Salmonella typhimurium. J Bacteriol 170 2078-2082 Friedmann HC (1975) Biosynthesis of corrinoids. In Babior BM (ed) Cobalamin ... 

Vitamin B12, P-Cyano(5, 6 -dimethylbenzimidazolyl)cobamide, or cyanocobalamin, has 181 atoms. Even disregarding the failures of semiempirical QM methods in application to very large molecular systems, mentioned in Section I, the attempt to model this system by any semiempirical method using a computer of the type IBM RISC/6000 failed because of the huge (minimal) basis set of 729 atomic orbitals. 

Cobalt is an essential element for bacteria, algae and ruminant mammals. For other organisms, including monogastric animals, cobalt is essential, in the form of the essential compound vitamin Bj2 (cobalamin). Rumen microflora of ruminants synthesises cobal-amin from cobalt in the diet. Derivatives of vitamin Bj2 cobamides are cofactors of some enzymes, for example of methyhnalonyl coenzyme A mutase, glutamate mutase and methionin synthetase. 

Brandt, L.J., Goldberg, L., Bernstein, L.H., and Greenberg, G. (1979) The effect of bacterially produced vitamin B analogues (cobamides) on the in vitro absoption of cyanocabalamin. Am J Clin Nutr 32, 1832-1836. 

Vitamin B12 chemistry. The structure of the 5,6-dimethylbenzimidazole-cobamide-coenzyme, as found in the wet crystals, has been determined by X-ray and neutron diffraction (see Figure 59) [123, 124]. A schematic... 

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