The use of penicillocarboxypeptidase-S1 in amino acid sequencing

The action of penicillocarboxypeptidase-S1 on a number of peptides obtained from enzymatic digests of penicillopepsin and other sources has been studied and compared with that of pancreatic carboxypeptidase A. In addition to proline, lysine, and arginine, penicillocarboxypeptidase-S1 readily cleaved glycine, and glutamic and aspartic acids from peptides which were hydrolyzed only slowly or not at all by carboxypeptidase A. Penicillocarboxypeptidase-S1 was also useful in locating the charges in peptides which contained several residues of aspartic and glutamic acids and their amides. The enzyme did not cleave γ-l-glutamyl bonds in synthetic peptides, but liberated γ-l-glutamyl-l-alanine from γ-l-glutamyl-γ-l-glutamyl-l-alanyl-γ-l-glutamyl-alanine. Although there were considerable differences in the rate at which different peptides could be degraded, this rate is not determined by the C-terminal amino acid alone. Generalizations cannot be made at this stage but it appears that some dipeptide sequences made up of two of the following-glycine, alanine, serine, threonine, and proline-were cleaved considerably more slowly than other bonds. Dipeptides with a free N-terminal were hydrolyzed very slowly, if at all. Peptides containing d-amino acids were not hydrolyzed. Penicillocarboxypeptidase-Sl appears to be a very useful enzyme in sequence work.