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Protease Enzyme

Proteolytic enzymes or proteases catalyses the breakdown of proteins into shorter polypeptides or amino acids. They undergo proteolysis by hydrolysing peptide bonds. Also, they are involved in various biological functions like protein catabolism, cell signalling and digestion.

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Protease Enzyme Definition

“Protease is an enzyme that catalyses the hydrolysis of peptide bonds present in proteins.”

In most of the living organisms, protease enzymes are essential for digestion and absorption of proteins.

Proteases or proteolytic enzymes are found in all living organisms, e.g. bacteria, algae, plants and animals and in some of the viruses too. They are involved in the catabolism and digestion of proteins and also in cell signalling.

Protease Enzyme Types

There are many different types of proteases, that take part in various biochemical processes.

On the basis of the site of the peptide bond cleavage, proteolytic enzymes are divided into two broad groups:

Exopeptidase: They catalyse the cleavage on terminal peptide bond, e.g. aminopeptidases, carboxypeptidases, etc.

Endopeptidase: They facilitate the cleavage of internal peptide bonds of proteins, e.g. pepsin, trypsin, chymotrypsin, elastase, etc.

Oligopeptidase refers to enzymes, that act on a specific peptide bond.

Different types of protease enzymes remain active in the different pH range, e.g. acid proteases, alkaline or basic proteases and neutral proteases.

Also see: Lipase Enzyme

Protease Enzyme Functions

Protease enzymes are essential for many biological processes. They are required for the regulation of various metabolic and cellular processes.

  • They are proteolytic, they help in digestion and catabolism of proteins. They catalyse the hydrolysis of peptide bonds and convert them to amino acids, which is then absorbed and utilised by cells.
  • They are required for the blood coagulation process.
  • Protease enzymes are involved in the cell division, growth, apoptosis and migration.
  • Protein recycling and transport across membranes.
  • They are involved in the activation of precursor proteins and zymogens.
  • Proteases provide immune support and regulate the process of tumour growth, metastasis, inflammation, etc.
  • They may help in wound healing and muscle soreness.

Protease Enzyme Examples

Here is the list of some of the important protease enzymes and their functions:

Protease Enzyme Name Function
Trypsin Found in pancreatic juice and breaks proteins and peptones and proteoses to dipeptides
Chymotrypsin Found in pancreatic juice and breaks proteins and peptones and proteoses to dipeptides
Carboxypeptidase Found in pancreatic juice and breaks proteins and peptones and proteoses to dipeptides
Elastase Present in pancreatic juice and digests elastin
Nuclease (ribonuclease and deoxyribonuclease) Present in pancreatic juice. They split nucleic acid to nucleotides
Collagenase It digests collagen
Dipeptidase Found in intestinal secretion. Breaks dipeptides to amino acids
Pepsin Present in stomach and converts proteins to smaller peptides – proteoses and peptones
Rennin Secreted by chief cells of the stomach and curdles milk protein
Thrombin Involved in blood coagulation
Plasmin Involved in blood coagulation
Renin Secreted by juxtaglomerular cells of the kidney and converts angiotensinogen to angiotensin
Hyaluronidase Present in the acrosome of sperms and helps in penetration of sperm into the ovum during fertilization
Insulinase Present in the kidney and liver. It degrades insulin
Chymases, tryptases They are present in mast cells and involved in allergic reactions and inflammation
Cathepsin, Neurolysin Present in immune cells

How does Protease work?

Proteolytic enzymes catalyse the hydrolysis of peptide bonds. Catalysis facilitates the nucleophilic attack of an activated water molecule on the peptide bond.

Serine, cysteine and threonine proteases function by forming an acyl-enzyme intermediate, which then gets hydrolysed by water to get the product and enzyme is set free.

Proteolytic enzymes range from general to specific, e.g. digestive protease enzyme, trypsin can cleave many proteins into smaller fragments, whereas enzymes like thrombin, which takes part in blood clotting are highly specific.

Many protease enzymes are present in an inactive form. Being proteins themselves, these precursors get converted to an active form by another protease enzymes. It helps in the regulation and control of the activity. E.g. trypsinogen, chymotrypsinogen, procarboxypeptidase, proelastase, etc.

Digestion of Proteins

Dietary protein is digested by many proteases enzymes present in the digestive tract. Pepsin present in the gastric juice as pepsinogen, which in presence of HCl, gets converted into pepsin. Pepsin partially hydrolyses proteins into proteoses and peptones. Gastric juice of infants contains renin, which hydrolyses milk protein. The partially digested proteins are acted on by pancreatic enzymes in the small intestine. Pancreatic secretion has many proteolytic enzymes present as an inactive precursor – chymotrypsinogen, trypsinogen, procarboxypeptidase. Enterokinase secreted by intestinal mucosa converts trypsinogen to trypsin, which in turn activates other proteolytic enzymes. Proteins, peptones and proteoses are acted on by pancreatic proteolytic enzymes to form dipeptides. The enzyme dipeptidase present in the succus entericus converts dipeptides to amino acids.

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Frequently Asked Questions

What is the role of protease enzymes?

Protease enzyme is a group of proteolytic enzymes, which hydrolyse the peptide bonds present in proteins to convert it to shorter polypeptides and amino acids. They play a major role in the digestion and absorption of dietary proteins. They also play a role in blood coagulation, support immunity, activation of precursor proteins, cell signalling, protein recycling, apoptosis, etc.

Where can proteolytic enzymes be found?

Proteolytic enzymes are found in both animals and plants. In humans, proteases are mainly present in pancreatic juice and gastric secretions to break down dietary proteins. Trypsin and chymotrypsin are secreted by the pancreas and pepsin is secreted by the chief cells in the stomach. Proteolytic enzymes are naturally found in various food sources such as roots, leaves and fruits of papaya contain papain, a protease enzyme. Pineapple fruits contain a proteolytic enzyme known as bromelain.

What fruit contains proteolytic enzymes?

Fruits like papaya, fig, pineapple, kiwi, etc. contain proteases. Proteases help in the digestion of proteins. Proteases from fruits are used as dietary supplements, treating wounds and also in food processing industries.

What is an example of a protease?

An example of a protease enzyme is pepsin. It is secreted by peptic of chief cells of gastric mucosa as a proenzyme called pepsinogen. Pepsinogen gets converted into pepsin by the action of HCl secreted by gastric glands. It converts proteins to short-chain polypeptides known as peptones and proteoses.

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