The Biosynthesis of Vitamin B 12 : A Study by 13 C Magnetic Resonance Spectroscopy

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Abstract
The origin of the methyl group on C-1 of Ring A of the corrin ring of vitamin B 12 was investigated by 13 C magnetic resonance spectroscopy. The proton-decoupled 13 C spectra of vitamin B 12 synthesized from [ 5 - 13 C]δ-aminolevulinic acid by Propionibacteria were obtained by Fourier-transform nuclear magnetic resonance of high resolution, and spectra of high-resolution proton magnetic resonance of the 13 C-labeled B 12 were also taken. The δ-carbon atom of δ-aminolevulinic acid is the source of seven or eight known positions of vitamin B 12 , depending on whether the C-1 methyl group is also derived from the labeled substrate. We have found seven resonances whose chemical shifts enable us to identify the position of the 13 C atoms in the molecule from the assignment of Dodderell and Allerhand. We observed no 13 C resonance corresponding to the C-1 methyl group of Ring A. Furthermore, the proton magnetic resonance spectrum showed no spin-spin splitting of the proton peak at the τ values assigned for the H atoms in this methyl group. It would thus appear that the methyl group at C-1, which has been considered to have the same origin as the δ-methine bridge of porphyrins, does not originate from the δ-carbon atom of δ-aminolevulinic acid. This finding may aid in elucidation of the mechanism of synthesis of the functional isomer of vitamin B 12 and porphyrins. The 13 C-labeled vitamin B 12 enabled us to make further assignments to the 13 C magnetic resonance of the vitamin.