Studies in the biosynthesis of vitamin B12

Abstract

The Pseudomonas denitrificans coba and the Salmonella typhimurium cbid genes were overexpressed in the heterologous E.coli system. The function of P.denitrificans coba gene product was identified as S-adenosyl methionine dependent methyl transferase catalyzing the C-2 and C-7 methylations of Uroporphyrinogen III to precorrin-2, without performing an extra methylation at C-12 of precorrin-2 to trimethylpyrrocorphin. The function of the S.typhimurium cbid gene product has not yet been identified. The C-terminus of the EColi cysg was shown to be a S-adenosyl methionine dependent methyltransferase catalyzing the C-2 and C-7 methylations of Uroporphyrinogen III to precorrin-2. The C-terminus of cysg was able to perform the extra methylation at C-12 of precorrin-2 to give trimethylpyrrocorphin. The C-terminus of cysg was not involved in the transformation of precorrin-2 to siroheme. The structures of the enzymatic reactions were identified by the use of 13C NMR.