Biological Chemistry - Berezov T. T., Korovkin B. F. 1998

Metabolism of Simple Proteins
Protein Digestion
Protein Digestion in the Intestine

Further Digestion of dietary Proteins takes place in the Small Intestine, where proteins are acted upon by Enzymes of the Pancreatic and Intestinal juices. Trypsin and Chymotrypsin act on proteins similarly to Pepsin, cleaving other internal peptide bonds; both enzymes are most active in a slightly alkaline medium (pH 7.2–7.8). Due to the hydrolytic action of all three Endopeptidases (pepsin, trypsin, chymotrypsin), Peptides of varying lengths and a certain amount of free Amino Acids are formed. Further Hydrolysis of peptides down to free amino acids is carried out by a group of enzymes known as peptidases. In addition to pancreatic carboxypeptidase, peptides are acted upon by intestinal aminopeptidase and various dipeptidases. This group of enzymes belongs to exopeptidases and catalyzes the hydrolysis of the peptide bond According to the scheme:

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The target of aminopeptidase is the peptide bond at the N-terminus of the peptide. Carboxypeptidase cleaves the peptide bond from the opposite C-terminus of the peptide. These enzymes successively cleave single amino acids from the polypeptide chain.

Ultimately, dipeptides remain, which are acted upon by specific dipeptidases, yielding free amino acids that are subsequently absorbed.

Other noteworthy Proteolytic Enzymes include pancreatic Elastase and collagenase, which hydrolyze Elastin and Collagen, respectively. Topographically, the main processes of protein digestion, much like those of CARBOHYDRATES and fats, occur On the surface of the intestinal mucosa (the so-called membrane digestion, according to A.M. Ugolev).