ATP-induced activation of the aminoacylation of tRNA by the isoleucyl-tRNA synthetase from Escherichia coli

The rate of aminoacylation of tRNA catalyzed by the isoleucyl-tRNA synthetase form Escherichia coli has been measured. A steady-state kinetic analysis of the rate as a function of the concentration of ATP gave nonlinear Hanes plots. ATP behaves as an activator of the reaction. The activation is observed at a low magnesium ion concentration and in the presence of spermidine. The presence of inorganic pyrophosphate or AMP enhances the activation. The results are consistent with a mechanism in which the binding of a second molecule of ATP increases the rate of dissociation of Ile-tRNA from the enzyme.