Trypsin

Trypsin is secreted by the pancreas in an inactive form trypsinogen. It is activated by enterokinase secreted by the glands in the intestinal wall. As trypsin is formed, it activates more trypsinogen to be converted into trypsin. This is autocatalytical activation. Trypsin acts in an alkaline medium between pH 7-9. It breaks a peptide bond next to basic amino acid like arginine or lysine. The polypeptide fragments are further digested by the exopeptidases. Carboxypeptidase requires the presence of zinc ion and trypsin.-Other exopeptidases are secreted in active form but need metal ions as cofactors to increase their activity. Figure illustrates the action of amino peptidase which removes terminal amino acids having free amino groups and carboxypeptidase which removes terminal amino acids possessing a free carboxyl group. In this way these two enzymes remove peptides from each end until a dipeptide fragment consisting of only two amino acids remains. Bonds between these pairs of amino acids are split by dipeptidases releasing free amino acid. The amino acids now, may be absorbed through the cells of the intestinal wall.

Figure: Breakdown of tripeptides