title: Characterization of a homogeneous complex of arginyl- and lysyl-tRNA synthetase: zinc and adenosine 5'-phosphate dependent synthesis of diadenosine 5',5'''-P1,P4-tetraphosphate.
abstract: Zinc, adenosine 5'-phosphate (AMP), and pyrophosphatase greatly stimulate the synthesis of diadenosine 5',5'''-P1,P4-tetraphosphate (Ap4A) by rat liver lysyl-tRNA synthetase. The synthesis of Ap4A does not require lysine; thus the lysyl-adenylate complex is not required. The substrates have been determined to be adenosine 5'-triphosphate (ATP) and AMP with apparent Km values of 2.1 mM and 1.5 mM, respectively. A zinc-dependent hydrolysis of ATP and AMP has been shown to be associated with the synthetase. In the presence of zinc there is a direct correlation between both the amount of AMP formed and the amount of Ap4A synthesized by lysyl-tRNA synthetase. Ap4A acts as a competitive inhibitor for ATP in the aminoacylation reaction of lysyl-tRNA synthetase with a KI of 2.5 microM. Concentrations of Ap4A up to 12.5 microM do not inhibit the synthesis of Ap4A by lysyl-tRNA synthetase. This suggests that there may be more than one binding site for ATP on the enzyme.
mesh_terms: D000227:Adenine Nucleotides / Q000096:biosynthesis* / Q000494:pharmacology; D000244:Adenosine Diphosphate / Q000494:pharmacology*; D000604:Amino Acyl-tRNA Synthetases / Q000378:metabolism*; D000818:Animals; D001126:Arginine-tRNA Ligase / Q000378:metabolism*; D015226:Dinucleoside Phosphates; D005260:Female; D007700:Kinetics; D008099:Liver / Q000201:enzymology*; D008250:Lysine-tRNA Ligase / Q000378:metabolism*; D046911:Macromolecular Substances; D051381:Rats; D015032:Zinc / Q000494:pharmacology*
chemical_list: D000227:Adenine Nucleotides; D015226:Dinucleoside Phosphates; D046911:Macromolecular Substances; C020733:diadenosine tetraphosphate; D000244:Adenosine Diphosphate; D000604:Amino Acyl-tRNA Synthetases; D001126:Arginine-tRNA Ligase; D008250:Lysine-tRNA Ligase; D015032:Zinc