Digestive enzyme

The digestive enzymes take part in digesting foods.

The digestive enzymes are synthesised by the digestive system and turn complex molecules into simple molecules which can be easily assimilated by the body. To do this they cleave specific chemical bonds. Each enzyme has its own specific substrate. There are three main types of these:

• proteolytic (which cleave proteins) ;
• glucolytic (which cleave carbohydrates) and ;
• lipolytic which cleave lipids).

Alpha-amylase digests starch and cleaves it into maltose and dextrin.

Lingual lipase is also found in infants in whom it helps to digest lipids from breast milk. They are found in adults but only play a minor role.

Pepsin (which is produced from pepsinogen) is an endoprotease which therefore cleaves proteins into peptides by breaking the peptide bonds involving aromatic amino acids (tryptophan, phenylalanine, tyrosine). It only acts with acid pH (between 1.8 and 4.4).

Gastric lipase hydrolyses short chain triglycerides into fatty acids and glycerol.

Pancreatic amylase cleaves plant starch into maltose.

Maltase, secreted by the mucosal cells, hydrolyses maltose into glucose in the brush border on the surface of epithelial cells lining the intestine.

Sucrase, lactase, maltase and isomaltase act on sucrose, lactose, maltose, and isomaltose respectively.

Trypsin, chymotrypsin, and carboxypeptidase cleave peptide bonds.

Pancreatic lipase breaks triglycerides down into glycerol and fatty acids.