Digestive enzymes are a group of enzymes that break down polymeric macromolecules into their smaller building blocks, in order to facilitate their absorption by the body. Digestive enzymes are found in the digestive tracts of animals (including humans) and in the traps of carnivorous plants, where they aid in the digestion of food, as well as inside cells, especially in their lysosomes, where they function to maintain cellular survival. Digestive enzymes of diverse specificities are found in the saliva secreted by the salivary glands, in the secretions of cells lining the stomach, in the pancreatic juice secreted by pancreatic exocrine cells, and in the secretions of cells lining the small and large intestines.

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.
  • Amylases split carbohydrates such as starch and sugars into simple sugars such as glucose.
  • Nucleases split nucleic acids into nucleotides.

What are Enzymes ?

Enzymes are biological molecules (typically proteins) that significantly speed up the rate of virtually all of the chemical reactions that take place within cells. They are vital for life and serve a wide range of important functions in the body, such as aiding in digestion and metabolism

In the human digestive system, the main sites of digestion are the oral cavity, the stomach, and the small intestine. Digestive enzymes are secreted by different exocrine glands including:

  • Salivary glands
  • Secretory cells in the stomach
  • Secretory cells in the pancreas
  • Secretory glands in the small intestine

Functions of Enzymes in Human Body

Enzyme Secreted by Function
Salivary Amylase (Ptyalin) Salivary Glands Converts starch to maltose
Renin Stomach Converts milk proteins to peptides
Pepsin Stomach Converts other proteins to peptides
Gastric Amylase Stomach Converts starch to maltose
Gastric Lipase Stomach Converts butter fat into fatty acids and glycerol
Trypsin Pancreas Converts proteins to peptides
Chymotrypsin Pancreas Converts proteins to peptides
Steapsin (Pancreatic Lipase) Pancrease Converts fats into fatty acids and glycerol
Carboxypolypeptidase Pancreas Converts peptides into amino acid.
Pancreatic Amylase Pancreas Converts starch to maltose
Entirokinase Small Intestine entirokinase activates trypsinogen to tryspsin.
Eripsin Small Intestine Converts polypeptides to amino acids.
Maltase Small Intestine Digests Maltose to glucose.
Sucrase Small Intestine Digests sucrose into glucose and fructose.
Lactase Small Intestine Digests lactose into glucose and galactose.

Uses of Enzymes in the Human Body

Food Digestion

The food you eat must to be broken down into its component nutrients to be absorbed and utilized by your body. Digestive system enzymes belong to a class of enzymes called hydrolases. These enzymes trigger a reaction called hydrolysis, which breaks large molecules into smaller units. There are many different digestive enzymes to break down different types of food components. For example, enzymes called pepsin and trypsin digest dietary proteins. Another hydrolase called lipase is secreted by your pancreas and helps break down dietary fats. The enzyme amylase stimulates the digestion of dietary starch.

DNA Copying

Your cells contain genetic material called chromosomes, each carrying an array of genes that encode your individual genetic makeup. This genetic material is in the form of a molecule called deoxyribonucleic acid, or DNA. When cells in your body divide, each newly created cell must contain an exact copy of your DNA. To carry out this copying, or replication, your body relies on specific enzymes. For example, enzymes called helicases and gyrases unwind the tightly coiled DNA strands so they can be copied. DNA polymerase enzymes participate in the actual copying process. DNA ligase enzymes are involved in finalizing the copying process.

Energy Production

Your body must generate energy to carry out all of its functions. Although blood sugar, or glucose, is the preferred fuel to generate energy, proteins and fats can also be used. These complex processes — collectively known as cellular respiration — rely on enzymes and generate molecules called adenosine triphosphate (ATP) that power your cells. For example, energy generation using glucose is called glycolysis. Each of the 10 steps in glycolysis involves a different enzyme. Each molecule of glucose broken down by glycolysis yields 2 ATP molecules. Examples of enzymes used in glycolysis include hexokinase, aldolase, enolase and pyruvate kinase. Other enzymes are involved in the generation of ATP from proteins and fats.

Enzymes and Human Health

Many medical conditions are associated with enzyme problems. For example, a deficiency of the digestive enzyme lactase, which breaks down milk sugar, leads to lactose intolerance. A more serious deficiency of digestive enzymes can develop with inflammation of the pancreas, or pancreatitis. This condition is often associated with weight loss and malnutrition due to a reduced ability to digest foods consumed in the diet. Inherited disorders can also cause enzyme defects that may have catastrophic consequences. For example, children born with Tay-Sachs disease have a genetic abnormality with an enzyme called beta-hexosaminidase A. The impaired function of this single enzyme leads to destruction of nerve cells in the brain and spinal cord. Children born with this disorder usually die in early childhood.