Categories of Digestive Enzymes

Categories of Digestive Enzymes

Hydrolysis of food nutrients in aqueous medium can occur on its own at a slow rate, but its rate is increased by organic catalysts in the alimentary canal. These catalysts are called digestive enzymes. These are present in the digestive juices secreted by the pancreas and by the digestive glands present in the wall of the alimentary canal.

Classification of Digestive Enzymes

Because digestive enzymes catalyze hydrolysis, they are all called hydrolases. According to the nutrients for which they catalyze water decomposition, they are further divided into four major categories-

1. Carbohydrate-Digestive Enzymes (Carbohydrases): They have two major subcategories -

• Amylases: Which degrade polysaccharide carbohydrates into disaccharides.
• Disaccharide-digesting enzymes: which break down disaccharides into monosaccharides. These are maltase, sucrase and lactase.

2. Proteinases or Proteolytic Enzymes: They have two major subcategories -

• Endopeptidases : They cleave large complex protein molecules into smaller fragments—proteoses → peptones → polypeptides by breaking them at the interstitial bonds. Among these, pepsin, erepsin, trypsin and chymotrypsin are prominent.
• Exopeptidases: They cleave the amino acid molecules located at their ends one by one by breaking the terminal bonds of the polypeptide chains and thus, gradually complete hydrolysis of these polypeptide chains. In these, carboxypeptidases react with the carboxyl group (—COOH) of the terminal bonds and aminopeptidases with the amino group (—NH2). Dipeptidases only break down dipeptides into their amino acid units.

3. Lipid-digesting enzymes (Lipases): They break down the ester bonds of fats and break them down.

4. Nucleases: They cleave nucleic acids into nucleotide monomers. These are of two types—RNA digesting ribonuclease and DNA digesting deoxyribonuclease.

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