Spontaneous, Metal-Catalyzed, and Enzyme-Catalyzed Decarboxylation of Oxalosuccinic Acid.
Abstract
Decarboxylation rates of oxalosuccinic acid, a tricarboxylic acid, has been studied in detail. It was shown that the keto forms of the acid spontaneously decarboxylate. The catalytic effect of three metals were examined. The overall effectiveness of the metals were Zn(2+) > Mn(2+) > Mg(2+). This catalysis resulted from the formation of a 1:1 complex between the acid and the metal ions. The enzyme isocitrate dehydrogenase (ICDH) was able to catalyze the reaction without the aid of a metal ion. Kinetically, protonated and deprotonated ICDH-oxas(3-) complexes were shown to exist. The effect of two divalent metals were studied. The rate constants for the Zn(2+)-ICDH-oxas(3-) and Mg(2+)-ICDH-oxas(3-) ternary complexes were nearly identical. It was also found that the Mg(2+) ternary complex could ionize (pK sub a=5.72) as well as the Mg(2+)-ICDH binary complex (pK sub a=7.64). It was concluded that (1) the actual binding site on the enzyme was different for each metal; and (2) the role of the metal ion is to create a more favorable geometry at the active site on the enzyme. This new geometry establishes a structure within the enzyme for other functional groups at the active site to better promote decarboxylation.
Document Details
- Document Type
- Technical Report
- Publication Date
- Jan 01, 1980
- Accession Number
- ADA092546
Entities
People
- Steven L. Sincoff
Organizations
- Air Force Institute of Technology