The biosynthesis of vitamin B 12 : a study by 13 C magnetic resonance spectroscopy.

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]delta-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 delta-carbon atom of delta-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 tau 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 delta-methine bridge of porphyrins, does not originate from the delta-carbon atom of delta-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.