[Role of ammonium nitrogen in the biogenesis of vitamin B12 by Propionibacterium shermanii]

Abstract

The effect of different nitrogen sources on the biosynthesis of vitamin B12 ano porphyrins by suspensions of resting cells of Propionibacterium shermanii was investigated. In the absence of ammonium nitrogen vitamin B12 was not accumulated by the bacterial cell. This was also the case when its nitrogen containing precursor--delta-aminolevulinic acid was added to the incubation medium. The porphyrins biosynthesis was not changed. When amino acids and their amides were used as the sole nitrogen source, an intensive formation of vitamin B12 developed, if the medium contained aspartic acid, asparagine and cystein subjected to distinct deamination, and glutamine. The study of the composition of extracellular tetrapyrrole compounds showed an accumulation of corrinoil with free carboxyl groups in the incubation medium in the absence of ammonium salts. This corrinoid was identical to cobyrinic acid with respect to its spectral characteristics and behaviour during electrophoresis in phosphate buffer. Possible pathways of the involvement of ammonium nitrogen and glutamine in the biosynthesis of vitamin B12 and the role of amide groups in the binding of corrinoids with cell proteins are discussed.