Influences of amino acid, ATP, pyrophosphate and tRNA on binding of aminoalkyl adenylates to isoleucyl-tRNA synthetase from Escherichia coli MRE 600.

Aminoalcohol-AMP esters, structurally related to the assumed intermediates of the amino acid activation reaction, behave as competitive inhibitors both with respect to the amino acid and ATP, when tested in the ATP-(32P) PPi-exchange or the tRNA-charging reaction. However, closer investigation of the binding of norvalinyl adenylate to isoleucyl-tRNA synthetase from Escherichia coli MRE 600 by an equilibrium method shows that only the amino acid is a true competitor, while ATP cannot displace the ester from binding. Pyrophosphate enhances the stability of the ester-enzyme complex whereas tRNA is without detectable influence.