Decarboxylation Reaction of Oxalacetic Acid by Metal Chelates. II. Metal-Amino Acid

Abstract

Decarboxylation of oxalacetic acid by metal chelates was investigated, using copper-(II) and manganese(II) as metals and seven amino acids, glycine, alanine, threonine, serine, glutamic acid, lysine, and histidine as ligands. All of the amino acids used here were of L form. When the concentration ratio of copper to the ligand was 1 : 1, all copper-amino acid systems showed more enhanced decarboxylation activity than that of copper(II) ion alone. In copper-amino acid, a linear relation was observed between pK_a of the amino acid and the decarboxylation rate of oxalacetic acid ; as pK_a values of both carboxyl and amino groups of the ligand became smaller, decarboxylation of oxalacetic acid became faster. Among the copper-amino acid systems, copper-histidine exhibited the fastest reaction rate, and, therefore, histamine and imidazole were also examined as the ligand in order to interpret the activity of histidine. Catalytic activity of manganese-amino acid was smaller than that of the corresponding copper-amino acid and the former did not show a clear relation observed in the latter. For copper-amino acid, a similar mode of the reaction was observed between decarboxylation of oxalacetic acid and hydrolysis of diisopropylphosphofluoridate.