Polypeptides. Part XIV. A comparative study of the stability towards enzymes of model tripeptides containing α-aza-amino-acids, L-amino-acids, and D-amino-acids
The stability of three model tripeptides, L-lysyl-α-aza-phenylalanyl-L-leucine, L-lysyl-L-phenylalanyl-L-leucine, and L-lysyl-D-phenylalanyl-L-leucine, towards aminopeptidase, carboxypeptidase, thermolysin, and trypsin has been investigated. These tripeptides were synthesised by the classical method of peptide synthesis. The α-aza-phenylalanine-containing tripeptide was stable to the first three of these enzymes, but the L-lysyl–α-aza-phenylalanine bond was readily cleaved by trypsin. The tripeptide containing D-phenylalanine was stable to all these enzymes, whereas the tripeptide with L-phenylalanine was completely cleaved in 72 h.