Each disaccharide has its own disaccharidase. For example, maltose is hydrolyzed by maltase , sucrose by sucrase , lactose by lactase , etc. Since the disaccharidases are on the surface of the epithelium, the final breakdown of carbohydrates occurs where the sugars will be absorbed. The pancreas secretes proteases in the form of zymogens that will be activated only in the lumen of the duodenum by the intestinal enzyme, enteropeptidase .
Trypsin catalyzes the conversion of more trypsinogen to trypsin.
Trypsin catalyzes the conversion of the other zymogens. The lining of the small intestine also secretes protein-digesting enzymes, aminopeptidase and dipeptidases . Aminopeptidase begins at the end of a polypeptide that has a free amino group and splits off one amino acid at a time. Dipeptidases attached to the intestinal lining split small polypeptides. Since the protein-digesting enzymes from the pancreas and small intestine break bonds in specific areas of the polypeptide, protein digestion to amino acids is a combined effort from all of these enzymes.