break peptide bonds between specific amino acids in the middle of polypeptide chains. They beak large polypeptides into smaller polypeptides.

Exopeptidases:

break peptide bonds at the ends of polypeptide chains, so producing amino acids.

Endopeptidases hydrolyse peptide bonds within the protein molecule, then exopeptidases hydrolyse the terminal or penultimate peptide bonds at the ends of these shorter peptides.

They break the peptide bonds joining amino acids together. The human intestine secretes a number of different proteases but they can be divided in two main types: endopeptidases and exopeptidases.

It forms a component of gastric juice which is secreted into the stomach; the hydrochloric acid also present in the juice initiates its activation.

The first - formed pepsin then quickly completes the conversion of the remainder of the pepsinogen, in a process known as autocatalysis.

Pepsin, which is an endopeptidase, hydrolyses proteins to be shorter-chain polypeptides.

It has a pH optimum of about 1.5 - 2.0; this provided by the hydrochloric acid.

It is activated to trypsin by the enzyme enterokinase secreted by epithelial cells of the villi; once formed, trypsin can autocatalyse the activation of more trypsinogen.

Like pepsin, trypsin is an endopeptidase which hydrolyses proteins to shorter-chain polypeptides.

It has a pH optimum of about 7.5 - 8.8; this is provided by alkaline salts present in bile and in pancreatic and intestinal juices.

They are found within the cell membranes of the microvilli found on the surface of intestinal epithelium cells, or in the cytoplasm of the epithelial cells.

They may be classified as aminopeptidases if they work at the end of the chain that has an amino acid with a free amino group or carboxypeptidases if they work at the opposite end where the amino acid has a free carboxyl group.