| Popis: |
Publisher Summary This chapter discusses the mechanism of carboxypeptidases used for structural studies, namely––pancreatic carboxypeptidases A and B. Carboxypeptidases are enzymes that remove amino acids one at a time from the C-termini of tripeptides, higher peptides, and proteins. The A enzyme (CPA) removes C-terminal aromatic and long side-chain aliphatic residues most rapidly, and removes glycine and acidic amino acids only slowly. The B enzyme has a narrower specificity, removing lysine and arginine rapidly, but it also removes neutral amino acids. Plant sources contain a carboxypeptidase (C) that removes C-terminal proline as well as many of the protein amino acids. The preparation of enzyme and sample is discussed. Chymotrypsin is the most likely contaminant and should be inactivated by treatment with diisopropyl phosphorofluoridate (DFP). The methods of examining the products of reaction of peptides with CPA and CPB are summarized. A guide to the rates of release of different amino acids by CPA is provided. The release of lysine by preparations of CPA is due to contamination with CPB or to inherent B-type activity. |
