Interacting Binding Sites of Isoleucyl‐tRNA Synthetase from Escherichia coli Studied by Equilibrium Partition

Abstract
The binding of tRNAIle to isoleucyl-tRNA synthetase [EC 6.1.1.5] in the presence of isoleucine or ATP was investigated using the equilibrium partition method. Isoleucine decreased the affinity of tRNAIle for the enzyme by a factor of .apprx. 5. The free standard energy of interaction was .apprx. 1 kcal/mol (4.2 kJ/mol). ATP exhibits qualitatively the same effect as isoleucine. A binding of 2 molecules isoleucine/molecule of enzyme could not be demonstrated, even in the presence of ATP and pyrophosphatase [EC 3.6.1.1].