Protease Enzyme

Protease enzyme catalyses the breakdown of proteins to shorter polypeptides or amino acids. They undergo proteolysis by hydrolysing peptide bonds.

Proteases are found in all the 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.

Protease Enzyme Function

Protease enzymes are essential for many biological processes. They are required for 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

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?

Protease 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.

Protease enzyme 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 protein 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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