The conversion of L-threonine to the Dg-1-amino-2-propanol of vitamin B12.

The recent formulation (1, 2) of the structure of vitamin Brz prompts us to report an investigation conducted several years ago on the origin of its aminopropanol component. Previous studies on the metabolism of L-threonine in rats had shown that it was cleaved mainly to acetate and glycine (3,4). The decarboxylation of threonine to the corresponding amine could not be demonstrated, within the limits of the experimental approach used, since there was no evidence for a significant conversion of threonine to a S-carbon acid such as propionic or pyruvic acid (3, 4). However, the discovery (5-7) of n,-1-amino-2-propanoll among the hydrolytic products of vitamin B1z suggested that the decarboxylation of L-threonine might occur in some organisms. In order to test this possibility, the biosynthesis of vitamin Brz was studied in the presence of L-threonine-N15. The aminopropanol showed a high incorporation of N l5, indicating the conversion of threonine to its corresponding amine. Although the decarboxylation of serine has long been known (8), this appears to be the first evidence for a decarboxylation of threonine.