Native Corrinoids from Clostridium cochlearium Are Adeninylcobamides: Spectroscopic Analysis and Identification of Pseudovitamin B 12 and Factor A

Abstract

ABSTRACT The corrinoids from the obligate anaerobe Clostridium cochlearium were extracted as a mixture of Co β -cyano derivatives. From 50 g of frozen cells, approximately 2 mg (1.5 μmol) of B 12 derivatives was obtained as a crystalline sample. Analysis of the corrinoid sample of C. cochlearium by a combination of high-pressure liquid chromatography and UV-Vis absorbance spectroscopy revealed the presence of three cyano corrinoids in a ratio of about 3:1:1. The spectroscopic data acquired for the sample indicated the main components to be pseudovitamin B 12 (Co β -cyano-7"-adeninylcobamide) (60%) and factor A (Co β -cyano-7"-[2-methyl]adeninylcobamide) (20%). Authentic pseudovitamin B 12 was prepared by guided biosynthesis from cobinamide and adenine. Both pseudovitamin B 12 and its homologue, factor A, were subjected to complete spectroscopic analysis by UV-Vis, circular dichroism, mass spectrometry, and by one- and two-dimensional 1 H, 13 C-, and 15 N nuclear magnetic resonance (NMR) spectroscopy. The third component was indicated by the mass spectra to be an isomer of factor A and is likely (according to NMR) to be 7"-[ N 6 -methyl]-adeninylcobamide, a previously unknown corrinoid. C. cochlearium thus biosynthesizes as its native “complete” B 12 cofactors the 7"-adeninylcobamides and two homologous corrinoids, in which the nucleotide base is a methylated adenine.