Exopeptidaasit

Exopeptidaasit, more commonly written as exopeptidases, are proteolytic enzymes that catalyze the hydrolysis of peptide bonds at the termini of peptide chains, removing amino acids one at a time from either the N-terminus or the C-terminus. They are distinguished from endopeptidases, which cleave peptide bonds within the interior of a protein or peptide. Exopeptidases are typically classified into aminopeptidases (N-terminal), carboxypeptidases (C-terminal), and dipeptidyl peptidases that remove dipeptides from the N-terminus.

Biochemical properties vary among exopeptidases. Many are metal-dependent metalloproteases (for example, zinc-containing carboxypeptidases), while others are serine proteases or belong to other catalytic families. Subcellular localization also differs: digestive exopeptidases such as pancreatic carboxypeptidases are secreted into the small intestine, intestinal aminopeptidases are often membrane-bound on the microvilli, and other exopeptidases exist as soluble enzymes in plasma or intracellular compartments.

Functions of exopeptidases are diverse. In digestion, they contribute to protein breakdown by trimming terminal amino acids to produce absorbable dipeptides, tripeptides, or free amino acids. They also participate in processing bioactive peptides and hormones, in antigen presentation by shaping peptide repertoires for MHC molecules, and in regulating peptide signaling and turnover within tissues.

Notable examples include aminopeptidase N (CD13), aminopeptidase A, and carboxypeptidases such as carboxypeptidase A and B. Dipeptidyl peptidase-4 (DPP-4) is a well-studied exopeptidase that cleaves dipeptides from N-termini and is a therapeutic target in type 2 diabetes.