R. A. Vishwakarma, S. Balachandran, A. I. D. Alanine, N. P. J. Stamford, F. Kiuchi, F. J. Leeper and A. R. Battersby
"Biosynthesis of Porphyrins and Related Macrocycles. Part 41. Fate of Oxygen Atoms as Precorrin-2 Carrying Eight Labelled Carboxyl Groups (13C18O2H) is Enzymatically Converted into Cobyrinic Acid"
J. Chem. Soc., Perkin Trans. 1,1993, 2893-2899. Full Text
5-Amino[1,4-13C2]laevulinic acid and 5-amino[1-13C]laevulinic acid are synthesised and all three 16O atoms of the latter are exchanged for 18O. The 13C,18O-labelled material is then converted in vitro into precorrin-2 by the combined action of four genetically overproduced enzymes. The product is isolated in its aromatised form, sirohydrochlorin and 13C-NMR shows that all 8 carboxyl groups retain both oxygen atoms throughout the biosynthesis. A cell-free enzyme preparation from Propionibacterium shermanii converts the 13C,18O-labelled sirohydrochlorin via precorrin-2 into cobyrinic acid, a late precursor of vitamin B12. 13C-NMR proves that 6 carboxyl groups of cobyrinic acid (b-g, inclusive) retain both oxygen atoms whereas the a-carboxyl group undergoes specific loss of one labelled oxygen atom.
Department of Chemistry
University of Cambridge