title: An investigation of the mechanism of activation of tryptophan by tryptophanyl-tRNA synthetase from beef pancreas.
abstract: Adenosine (S)-5'-[alpha-17O, 18O2]triphosphate has been synthesized and used to investigate the stereochemical course of activation of tryptophan by tryptophanyl-tRNA synthetase from beef pancreas. It is shown that the reaction proceeds by displacement of Mg pyrophosphate from MgATP with inversion of configuration at P alpha. Tryptophanyl-tRNA synthetase catalyses positional isotope exchange in adenosine 5'-[beta-18O2]triphosphate in the presence of tryptophan but not in its absence or in the presence of the competitive inhibitors tryptamine and tryptophanol. These observations eliminate a multi-adenylyl transfer or dissociative mechanism and in combination with the sterochemical study leave a direct associative 'in line' displacement at P alpha of MgATP as the only tenable mechanism for the activation of tryptophan by tryptophanyl-tRNA synthetase.
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000604:Amino Acyl-tRNA Synthetases / Q000378:metabolism*; D000818:Animals; D001711:Biotransformation; D002384:Catalysis; D002417:Cattle; D055598:Chemical Phenomena; D002621:Chemistry; D009682:Magnetic Resonance Spectroscopy; D010103:Oxygen Isotopes; D010179:Pancreas / Q000201:enzymology*; D013237:Stereoisomerism; D014364:Tryptophan / Q000378:metabolism*; D014369:Tryptophan-tRNA Ligase / Q000378:metabolism*
chemical_list: D010103:Oxygen Isotopes; D014364:Tryptophan; D000255:Adenosine Triphosphate; D000604:Amino Acyl-tRNA Synthetases; D014369:Tryptophan-tRNA Ligase