pNon-enzymic transamination reactions at 85° between various amino acids and α-oxoglutaric acid are catalysed by metal ions, e.g. Alsup3+/sup, Fesup2+/sup, Cusup2+/sup and Fesup3+/sup. The reaction is optimum at pH4·0. Of the 14 amino acids studied histidine is the most active. In the presence of Alsup3+/sup histidine transaminates with α-oxoglutaric acid, forming glutamic acid and Alsup3+/sup–imidazolylpyruvic acid complex as the end products. However, in the presence of Fesup2+/sup or Cusup2+/sup the products are glutamic acid and a 1:2 metal ion–imidazolylpyruvic acid chelate. The greater effectiveness of histidine in these reactions is attributed to the presence of the tertiary imidazole nitrogen atom, which is involved in the formation of stable sparingly soluble metal ion–imidazolylpyruvic acid complexes or chelates as end products of these reactions. Of the metal ions studied only Alsup3+/sup, Fesup2+/sup, Fesup3+/sup and Cusup2+/sup are effective catalysts for the transamination reactions, and EDTA addition completely inhibits the catalytic effect of the Alsup3+/sup. Spectrophotometric evidence is presented to demonstrate the presence of metal ion complexes of Schiff bases of histidine as intermediates in the transamination reactions. These results may contribute to understanding the role of histidine in enzyme catalysis./p
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