Phenylalanyl‐tRNA Synthetase from Escherichia coli K10

A synergistic coupling was observed for ligands binding to the specific sites for l‐phenylalanine and ATP. Dissociation constants were measured by the use of fluorescence titration and equilibrium dialysis techniques. It is found that l‐phenylalanine, l‐phenylalanine methylester, and phenylethylamine bind with an increased affinity when ATP, ADP, AMP or adenosine were present. With l‐phenylalanine, synergistic binding was only observed for adenosine; ATP has probably no effect. Results of competition experiments, the stoichiometry of complex formation and the magnitude of dissociation constants indicate that synergistic coupling involves the binding sites for ATP and amino acid at the active site.