A stereochemical and positional isotope exchange study of the mechanism of activation of tyrosine by tyrosyl-tRNA synthetase from Bacillus stearothermophilus

Tyrosyl-tRNA synthetase from Bacillus stearothernwphilus catalyses the activation of ¹⁸O₂]-tyrosine by adenosine 5$\text{?}$(R)α-¹⁷O]triphosphate with inversion of configuration at P_α. It also catalyses positional isotope exchange in adenosine5$\text{?}$(β-¹⁸O₂]triphosphate in the presence of tyrosine, but not in its absence or in the presence of the competitive inhibitor tyrosinol. Together these results imply that the enzyme catalyses an associative “in line” displacement of pyrophosphate from P_α of ATP by tyrosine.