Digestive enzymes are diverse and are found in the saliva secreted by the salivary glands, in the stomach secreted by cells lining the stomach, in the pancreatic juice secreted by pancreatic exocrine cells, and in the intestinal (small and large) secretions, or as part of the lining of the gastrointestinal tract.
Digestive enzymes are classified based on their target substrates:
proteases and peptidases split proteins into small peptides and amino acids.
lipases split fat into three fatty acids and a glycerol molecule.
carbohydrases split carbohydrates such as starch and sugars into simple sugars such as glucose.nucleases split nucleic acids into nucleotides.