Glutamyl Transfer Ribonucleic Acid Synthetase of Escherichia coli

Escherichia coli glutamyl transfer ribonucleic acid synthetase acylates the three homologous tRNAglu isoacceptors with very similar Km values (2.4 to 4.6 x 10-7 m). The pure enzyme forms a 1:1 complex with its cognate tRNA as judged by gradient centrifugation and fluorescence-quenching studies. The biological specificity of complex formation is not strictly observed in vitro since fluorescence-quenching studies demonstrate complexes of this enzyme with Escherichia coli tRNAval and tRNAleu. Studies on the protection by tRNAglu against heat inactivation of the enzyme give a binding constant of 3.6 x 10-7 m for this interaction. Experiments performed in this paper indicate a concerted mechanism of glutamyl-tRNA formation.