Non-enzymic β-decarboxylation of aspartic acid

Non-enzymicβ-decarboxylation of aspartic acid at 85° is catalyzed by Al(3+) and pyridoxal. The reaction is optimum at pH 4.0. Both Al(3+) and pyridoxal are specifically required because replacing these by other cations or by other vitamin B6 derivatives greatly lowers the formation of alanine. Conversion of 8 µmoles of aspartic acid to alanine is optimum in presence of 1µmole of Al(3+) and 5 µmoles of pyridoxal. Increasing the concentration of pyridoxal to more than 5 µmoles lowers the alanine formation by the latter being converted to pyruvate by transamination with the excess pyridoxal.Studies on the mechanism of decarboxylation suggest that aspartic acid is first converted to oxalacetic acid by transamination with pyridoxal which in turn is converted to pyridoxamine. This is followed by decarboxylation of oxalacetic acid to form pyruvic acid which transaminates with pyridoxamine to form alanine. The results are interpreted to suggest that the non-enzymic aspartateβ-decarboxylation process is closely related to and inseparable from the non-enzymic transamination process in a manner analogous to that reported for the highly purified asparateβ-decarboxylase. The possible significance of these results to prebiotic molecular evolution is briefly discussed.