Spectroscopic studies on the formation of metal complexes and rate studies on the metal catalyzed decarboxylation of oxaloacetate and its esters indicate tbat oxaloacetate, in the presence of metal ions, decarboqlates according to the mechanism of Steinherger and Westheimer [9]. Factors which favor this reaction me&a&m enhance the rate of decarboxylation. Although the catalytic efficiency of oxaloacetate decarboxylase (OAD) can be accounted for by the enhancement factors deduced from the nonenzymic systems, this does not guarantee that the two systems react by an identicai mecbankm. Oxaloacetic acid has been shown to decarbosq4ate spontaneously [l-3] and catalytically by the action of t&n&ion and lanthanide ions [l, 4-61 and in the presence of an enzyme, oxaloacetate decarboxylase (OAD, o?raloscetate-4-carboxy-lase, EC 4.1.1.3) [7, S]. Because of the role of a metal ion in the enzymic reaction and its function as a catalyst for the chemical reaction, the metal-catalyzed decarhoxylation of cr ,~~-dimethyl oxaloacetic acid has been studied extensively with a view that it may serve as a chemical model for the enzymic reaction 19, lo]. Since the usefulness of a chemical model depends on a satisfactory extrapolation of the analogy of a chemical system to the enzymic system, the metal-catalyzed decarboxylation of oxaloacetic acid, n-hich is the natural substrate of OAD, may represent a better model for the enzymic reaction. Attempts were, therefore, made to elucidate the reaction mechanism by spectroscopic methods and to seek factors Khich are responsible for the enhancement of rates of the metal-catalyzed decarboxylation of oxaloacetic acid. Results are discussed in terms of the usefulness and scope of the met&catalyzed reaction as the chemical model for the OAD-cataJyzed reaction. EXPERIMENTAL Melting points were determined on a Fisher-John hot stage apparatus. Sodium acetate (0.15 M) buffers, pH 3.5 and 5.1 were prepared according to Gomori [II] and pH measured with a Radiometer 'T'MYC.