Abstract
It has been reported that DBCC is readily decomposed by illumination to hydroxocobalamin and adenosine-5'-aldehyde or adenosine-5'-carboxylic acid under aerobic conditions and 8,5'-cyclic adenosine under anaerobic conditions. The finding that methylcobalamin acts as a methyl donor in methionine formation leads a hypothesis that a fission of Co-C linkage followed by a ligand exchange takes an important role in the coenzyme action of DBCC. This paper deals with the photochemical decomposition of Co-β, γ-dihydroxypropylcobalamin, synthesized previously by the authors, (1) under the bubbling of air, (2) in the presence of dissolved oxygen, (3) in the nitrogen atmosphere, and (4) in the presence of NaBH_4. The irradiation products formed from the dihydroxypropyl group were as follows : (1) glyceric acid, (2) glyceraldehyde and glycerol, (3) glycerol and a small amount of an unidentified substance and, (4) glycerol. The decomposition routes of dihydroxypropylcobalamin under the aerobic conditions is considered to be analogous to those of DBCC. The formation of glycerol is not consistent with the formation of 8,5'-cyclic-adenosine but is similar to the formation of methanol in the photochemical decomposition of methylcobalamin reported by Weissbach et al. The reaction mechanism may be interpreted on the formation of vitamin B_<12r> and dihydroxypropyl free radical by the homolytic fission of Co-C bond.
