RECOGNITION OF TRNA BY ISOLEUCYL-TRNA SYNTHETASE - EFFECT OF SUBSTRATES ON DYNAMICS OF TRNA-ENZYME INTERACTION

An interaction between the isoleucine catalytic site and the tRNA recognition site of isoleucyl-tRNA synthetase (Escherichia coli) was detected using an assay for the binding of tRNA to enzyme. The effect of isoleucine is to increase the rate at which tRNA enters and leaves its binding site by sixfold without, therefore, a large effect on the equilibrium constant for tRNA binding. This effect requires neither transfer of isoleucine to tRNA nor activation of isoleucine as isoleucyl-AMP; the binding of isoleucine alone suffices. It appears from these data that release of aminoacyl-tRNA is the rate-limiting step in the acylation, or transfer, reaction. The apparent maximum rate constant for association of tRNA and enzyme is relatively large, 6 × 106 m-1 sec-1 (17 °C). © 1969.