Abstract

101
K. Ichinose, M. Kodera, F. J. Leeper and A. R. Battersby
"Biosynthesis of porphyrins and related macrocycles. Part 51. Proof that a reductive step occurs during the biosynthesis of vitamin B₁₂ by the micro-aerophilic organism, Propionibacterium shermanii"
J. Chem. Soc., Perkin Trans. 1,1999, 879-887. Full Text

5-Amino[4-¹³C]laevulinic acid has been synthesised for enzymic conversion into ¹³C-labelled precorrin-2. This was incubated with an enzyme system from Propionibacterium shermanii in the presence of [4-²H₂]NADH and [4-²H₂]NADPH to yield cobyrinic acid, shown to carry ²H at C-19 by appropriate ¹³C-NMR studies. The same reducing cofactors but now stereospecifically labelled at C-4 with tritium were similarly used to biosynthesise cobyrinic acid which was ³H-labelled from the 4(R)-cofactors but carried no ³H when the 4(S)-cofactors were used. Suitable degradation of the cobyrinic acid after conversion into its ester proved ³H-labelling at C-19. These results establish that the biosynthesis of vitamin B₁₂ in the microaerophilic organism Pr. shermanii involves a reductive step in which a reductase enzyme transfers 4-H_R of the cofactor to C-19 of the macrocycle.

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