The effects of thiamine hydrochloride and its decomposed solution on the stabilities of cobalamins under anaerobic conditions were investigated, and the latter one was confirmed to hasten the degradation of cobalamins more strongly than the former one. Among the various decomposed compounds of thiamine hydrochloride, pyrimidine moieties showed no effect, mercaptopropyl alcohol and thiazole moiety showed little effect, but formic acid showed a strong effect on the degradation of hydroxocobalamin. The other organic acids such as acetic, propionic and butyric acid had no effect on the degradation of hydroxocobalamin. In addition, the reaction between formic acid and hydroxocobalamin was observed in detail, and the following results were obtained. (1) Hydroxocobalamin was strongly degradated between pH 5 and pH 7 at low temperatures by formic acid. (2) The brownish yellow degradated solution of hydroxocobalamin had an absorption maximum at 460mμ, but the B12r, the reduced form of vitamin B12, was not found in it. (3) Formic acid was also decomposed when it accelerated the decomposition of hydroxocobalamin. From these observations we may suppose that formic acid was decarboxylated by the cobalt of hydroxocobalamin.
