title: Mechanism of activation of phenylalanine and synthesis of P1, P4-bis(5'-adenosyl) tetraphosphate by yeast phenylalanyl-tRNA synthetase.
abstract: The activation of L-phenylalanine by yeast phenylalanyl-tRNA synthetase using adenosine 5'-[(S)-alpha-17O,alpha,alpha-18O2]triphosphate is shown to proceed with inversion of configuration at P alpha of ATP. This observation taken together with the lack of positional isotope exchange when adenosine 5'-[beta,beta-18O2]triphosphate is incubated with the enzyme in the absence of phenylalanine and in the presence of the competitive inhibitor phenylalaninol indicates that activation of phenylalanine occurs by a direct "in-line" adenylyl-transfer reaction. In the presence of Zn2+, yeast phenylalanyl-tRNA synthetase also catalyzes the phenylalanine-dependent hydrolysis of ATP to AMP and the synthesis of P1,P4-bis(5'-adenosyl) tetraphosphate (Ap4A). With adenosine 5'-[(S)-alpha-17O,alpha,alpha-18O2]triphosphate, the formation of AMP and Ap4A is shown to occur with inversion and retention of configuration, respectively. It is concluded that phenylalanyl adenylate is an intermediate in both processes, Zn2+ promoting AMP formation by hydrolytic cleavage of the C-O bond and Ap4A formation by displacement at phosphorus of phenylalanine by ATP.
mesh_terms: D000227:Adenine Nucleotides / Q000096:biosynthesis*; D000604:Amino Acyl-tRNA Synthetases / Q000378:metabolism*; D015226:Dinucleoside Phosphates; D009682:Magnetic Resonance Spectroscopy; D008968:Molecular Conformation; D010103:Oxygen Isotopes; D010649:Phenylalanine / Q000378:metabolism*; D010652:Phenylalanine-tRNA Ligase / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000201:enzymology*; D046249:Transfer RNA Aminoacylation
chemical_list: D000227:Adenine Nucleotides; D015226:Dinucleoside Phosphates; D010103:Oxygen Isotopes; D010649:Phenylalanine; C020733:diadenosine tetraphosphate; D000604:Amino Acyl-tRNA Synthetases; D010652:Phenylalanine-tRNA Ligase