Corrinoids incomplete

Natural Bn-derivatives can occur either as complete corrinoids where a nucleotide fimction is attached to the propionic acid substituent at Cl7, or as incomplete corrinoids, which lack the nucleotide fimction and generally represent biosynthetic intermediates on the way to the complete corrinoids [23, 29]. 

By adding a cell extract of the parental strain P. shermanii to the culture of 30 the synthesis of vitamin Bn was restored, although incompletely. The activity of ALA synthetase and ALA dehydratase in the strain 30 was not reduced, the rate of PBG synthesis was normal, therefore, the block in corrinoid synthesis occurred at a step distal to PBG formation, where the pathways of porphyrin and corrinoid synthesis diverge. It should be noted that the ratio of propionic to acetic acid in negative mutants remained in the range of 2 1 formic acid was produced only by two cultures, 30 and rough. Mutant 9 produced a low level of acetic acid, and volatile acids were represented basically by propionic acid alone. 

The corrin ring and the nucleotide moiety are synthesized only by bacteria and some algae, but the cobalt-binding p-ligands can be introduced by some enzymatic systems in animals and humans. The synthesis of precursors in adequate amounts is often impaired, that is why microorganisms, in addition to the biologically active forms, also contain incomplete forms of corrinoids, mainly those in which the nucleotide moiety is lacking cobyric acid, cobinamide, cobinamide-P and cobinamide-GDP. Under conditions unfavorable for the synthesis of the nucleotide moiety incomplete forms may predominate, especially cobinamide. The content of complete forms increases in old (or aerated) cultures at the expense of incomplete forms. 

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. 

Biosynthesis of vitamin Bn by propionic acid bacteria, as we have seen (Section 4.4.5), almost parallels growth under anaerobic conditions. Vitamin Bn accumulates in the cell (the above-mentioned case of vitamin Bn secretion apparently is peculiar to a single mutant strain) mainly as coenzyme forms of incomplete corrinoids. These features are taken into account in the industrial production of vitamin Bn. The culture is grown anaerobically, in a medium containing glucose, corn-steep liquor, ammonium sulfate, and a cobaltous salt, since Co is part of the vitamin Bn molecule. Acids formed by the culture are continuously neutralized with a solution of NaOH or (NH4)20H. 

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