karboksypeptidaasit

Karboksypeptidaasit (carboxypeptidases) are exopeptidases that remove single amino acids from the carboxyl terminus of peptide chains. They are zinc-dependent metalloenzymes that participate in protein digestion as well as in the maturation and turnover of peptides. They are widely distributed among animals, plants and microbes and can be secreted or localized to intracellular compartments.

In mammals the best characterized members are pancreatic carboxypeptidases A and B. Pancreatic carboxypeptidases A (CPA1, CPA2) preferentially remove hydrophobic C-terminal residues, while carboxypeptidase B (CPB1) tends to cleave basic residues such as arginine and lysine. Additional mammalian carboxypeptidases include tissue-associated forms such as carboxypeptidase M and enzymes involved in prohormone and neuropeptide processing, including carboxypeptidase E and related isoforms. Some organisms also express carboxypeptidase Z and other family members with distinct tissue distributions and substrate specificities.

Biochemical characteristics and mechanism: carboxypeptidases require a catalytic zinc ion coordinated by histidine and other residues within an active site motif, commonly HEXXH, to activate a water molecule for nucleophilic attack on the peptide carbonyl. Many pancreatic enzymes are synthesized as inactive zymogens and activated in the intestinal lumen by proteolytic cleavage. Their activity is modulated by pH, ionic conditions and, in some cases, specific inhibitors or metal chelators.

Functions and significance: karboksypeptidaasit participate in digesting dietary proteins, but also in processing and inactivation of peptide hormones and neuropeptides. Their proper function supports protein turnover and peptide signaling, whereas dysregulation can be related to digestive disorders or altered peptide maturation in disease contexts.