Peptide Acceptors in the Arginine Transfer Reaction

To determine whether small peptides could function as acceptors in the reaction catalyzed by arginyl-tRNA-protein transferase they were tested for their ability to inhibit the transfer of [14C]arginine from tRNA to bovine albumin and reaction mixtures containing them were examined by paper electrophoresis for the presence of new radioactive products. Among di- and tripeptides containing 17 different NH2-terminal residues only those with glutamic acid, aspartic acid, and, to a lesser extent, cystine were inhibitory. Inhibition was competitive with albumin and associated with the peptide-dependent formation of a new radioactive product. When Glu-Ala was used as inhibitor the product was isolated and identified as Arg-Glu-Ala. A marked variation in Ki values was observed for different di- and tripeptides containing appropriate NH2-terminal residues, suggesting that in addition to an NH2-terminal dicarboxylic amino acid other residues influence substrate specificity in this reaction. Certain non-peptide derivatives of the dicarboxylic acids were also found to serve as acceptors. Isoasparagine and isoglutamine were the best substrates among these compounds and acceptor specificity was related to the presence of a blocked α-carboxyl and an unsubstituted β- or γ-carboxyl group.