[Increasing specificity of tryptophanyl-tRNA synthetase after amino acid activation]

It is shown for beef pancreas tryptophanyl-tRNA synthetase that there exists a mechanism which provides additional discrimination in vitro after misactivation of monofluorinated tryptophan analogs. In the presence of tryptophan one can observe a rapid decomposition of noncognate aminoacyl adenylate-enzyme complexes containing 4-fluoro-, 6-fluoro- or 7-fluorotryptophan residues, whereas the stoichiometry aminoacyl adenylate.enzyme complexes with tryptophan and 4-fluorotryptophan residues is not changed. Rejection of noncognate aminoacyl adenylate-enzyme complexes is connected neither with the enzymatic hydrolysis of aminoacyl adenylate nor with the competition of non-cognate aminoacyl adenylate and the added amino acid for the enzyme binding site. Rejection of noncognate complexes is presumably caused by the interaction between the active centers localized on two subunits, with one of them being occupied by an amino acid molecule and the other one by noncognate aminoacyl adenylate.