Peptide Acceptors in the Leucine, Phenylalanine Transfer Reaction

Defined di-and tripeptides were tested as acceptors in the reaction catalyzed by leucyl , phenylalanyl-tRNA -protein transferase.Criteria for acceptance were ability to inhibit the crsi-casein-dependent enzymatic transfer of i4C-amino acid from tRNA to protein and the presence in reaction mixtures of a specific peptide-dependent radioactive product.Among peptides comprising 19 ditferent NHz-terminal residues, only those with arginine, lysine and, to a lesser extent, histidine fuhllled these criteria.Results were similar using phenylalanyl or leucyl-tRNA.Inhibition was found to be competitive with crsr-casein.When Lys-Ala-Ala was used as acceptor for phenylalanine, the product was isolated and identified as Phe-Lys-Ala-Ala.All peptides containing an NHz-terminal L-arginine or L-lysine residue were found to function as acceptors; how- Peptide Arg-Lys.....