Glutamyl Transfer Ribonucleic Acid Synthetase of Escherichia coli

Escherichia coli glutamyl transfer ribonucleic acid synthetase acylates the three homologous tRNAGIU isoacceptors with very similar K, values (2.4 to 4.6 X lop7 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 tRNAG l” against heat inactivation of the enzyme give a binding constant of 3.6 X lo-’ M for this interaction. Experiments performed in this paper indicate a concerted mechanism of glutamyl-tRNA formation.