The coenzymic and chemical properties of a carbocyclic analogue of vitamin G 12 coenzyme.

An analogue of vitamin Blz coenzyme in which the ribosyl oxygen has been replaced by -CH2has been synthesized. This compound has spectral properties very similar to vitamin Blz coenzyme. The chemical properties of the analogue differ from those of vitamin B1e coenzyme in that reaction with CNand BH4does not result in cleavage of the carboncobalt bond. The analogue functions as coenzyme in the reaction catalyzed by dioldehydrase. The reaction in the presence of analogue is one-third as fast as with the coenzyme. Other properties of the enzymic reaction in the presence of the analogue are similar to those observed with the coenzyme: spectral changes in the presence of substrate and glycolaldehyde, hydrogen exchange between substrate and coenzyme, and over-all deuterium isotope effect. It was concluded that the ribosyl oxygen of the coenzyme cannot play an essential role in the catalytic process.