procarboxypeptidasesare

Procarboxypeptidases are zymogens that serve as inactive precursors to the digestive enzymes carboxypeptidase A and carboxypeptidase B. They are produced by pancreatic acinar cells and secreted into the pancreatic juice in their inactive proforms. The main purpose of the proenzyme form is to prevent premature proteolysis within the pancreas.

Activation occurs in the small intestine. The enzyme enteropeptidase converts the pancreatic zymogen trypsinogen to trypsin, and then trypsin activates procarboxypeptidase A and procarboxypeptidase B by cleaving their N-terminal propeptides. This proteolytic activation converts them into mature, active carboxypeptidases, which participate in protein digestion.

Functionally, active carboxypeptidase A and B are exopeptidases that cleave single amino acids from the C-terminus of peptide substrates. Carboxypeptidase A has a preference for bulky hydrophobic C-terminal residues such as phenylalanine, tyrosine, and tryptophan, whereas carboxypeptidase B favors basic residues like lysine and arginine. Both enzymes are zinc metallopeptidases and require proper folding and activation to achieve catalytic activity.

Physiological role and regulation are centered on facilitating complete protein digestion in the small intestine. The proenzyme strategy protects pancreatic tissue from autodigestion, while the cascade of proteolytic activations ensures enzymes become active only after reaching the digestive tract. In laboratory and clinical contexts, understanding procarboxypeptidase activation informs studies of pancreatic function and digestive disorders.