How Do Proteases Work? Key Functions and Examples
There are different enzymes produced by our gastrointestinal system and in cells for the various biochemical functions. One such type is a protease. It is a genre of protein-digesting enzyme found in different chemical shapes. In this article, we will study the different types of proteolytic enzymes and their respective functions.
The enzyme that reduces the complex protein molecules into smaller chains of polypeptides (amino acids) for easier assimilation is called protease. A protease enzyme catalyzes and breaks down the peptide bonds present in bigger protein molecules to reduce them into constituent amino acids. It is a process of digestion that takes place in our stomach and small intestine.
There are different kinds of protein-digesting enzymes with distinct functions. This type of enzyme can also be found in other primitive and advanced animals. The most essential function is to digest and break down protein into smaller units for easier assimilation.
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Types of Protease Enzyme
The proteolytic enzymes list can be segmented into three broader groups in terms of their mechanism and site of action.
Endopeptidase
This type of proteolytic enzyme acts on the peptide bonds presents internally in the protein molecules. It helps in breaking down macromolecules of protein by dissociating the internal peptide bonds to form smaller polypeptide units. example - trypsin, pepsin, elastase, chymotrypsin, etc.
Exopeptidase
This type of protease enzyme acts on the terminal peptide bonds and dissociates the amino acids present at the end of protein molecules. Example - carboxypeptidases, aminopeptidases, etc.
Oligopeptidase
According to its protease definition, this enzyme acts on specific amino acid bonds in a protein and performs catalysis.
Mechanism of Action of Protease
As mentioned earlier, the proteolytic enzymes act on the peptide bonds in a protein molecule and hydrolyze them to form smaller polypeptide molecules for absorption. The process is facilitated by activating a water molecule in the peptide bond and then catalyzing it to break.
The protease function depends on the mechanism of action. For instance, cysteine, serine, and threonine hydrolyzing enzymes form an acyl-enzyme as an intermediate and then hydrolyze in presence of water to get the product. The enzymes in this action are set free once the hydrolysis is done.
Apart from digestive enzymes, there are proteases taking part in other biochemical reactions. For instance, thrombin participates in blood clotting reactions. On the other hand, trypsin cleaves protein molecules to form smaller molecules of polypeptides for easier absorption in the digestive system.
The digestion of protein present in our diet takes place in different phases considering the locations. Pepsin is one of the proteolytic enzymes examples present in gastric juice. It comes out as pepsinogen, an inactive form of this enzyme. Due to the acidic environment in the stomach, it gets converted into pepsin by the influence of HCl. The partial hydrolysis of protein takes place in the stomach to form peptones.
Peptones then reach the small intestine where the proteases act in an alkaline environment. The bile salts convert the acidic chyme of the stomach into an alkaline one. In this environment, the inactive precursors such as trypsinogen, chymotrypsinogen, and procarboxypeptidase are activated to form trypsin, chymotrypsin, and carboxypeptidase respectively. Trypsin functions as a precursor to activate other proteolytic enzymes and the rest of the protein digestion take place.
In the small intestine, peptones, proteoses, and protein macromolecules are then digested to form polypeptide molecules. This process can also take place further to dissociate polypeptides to produce amino acids. Dipeptidase is an enzyme that functions as a hydrolytic agent to produce amino acids.
Application of Protease Enzyme
These enzymes are highly essential for the digestion of protein to produce absorbable polypeptides. These polypeptides are used in different biological processes.
The applications of proteases are:
The breakdown of protein into polypeptides is done by the proteolytic enzymes in the digestive system of higher-order animals. These enzymes can be found in unicellular animals performing the same function at the cellular level.
The catabolic process leads to the formation of amino acids. These structural units of protein are used for creating specific proteins according to the need of cells.
Specific proteases are required to conduct blood coagulation.
These enzymes are also used in the growth, cell division, migration, and apoptosis.
Another important function of these enzymes is to recycle protein and to produce smaller units for easier transportation through the cell membranes.
Some of the proteases act as precursors for other proteolytic enzymes. Some activate precursor zymogens and proteins.
They also regulate tumor growth, inflammation, and metastasis and support the immune system.
They also aid in healing wounds and cure soreness in muscles.
This is all you need to know to answer what is proteolytic enzyme. Study the different types of proteases and their specific functions with examples. Find out the locations of secretion of these enzymes and correlate with their functions.
FAQs on Protease: Meaning, Types, and Mechanism
1. What is a protease and what is its primary function?
A protease is a type of enzyme that catalyses proteolysis, which is the breakdown of proteins into smaller polypeptides or single amino acids. Its primary function is to hydrolyse (break) the peptide bonds that link amino acids together in a protein chain. This is a crucial process for biological functions like digestion, cell regulation, and blood clotting.
2. What are the main types of proteases based on their catalytic mechanism?
Proteases are primarily classified into several major types based on the key amino acid or molecule at their active site:
Serine Proteases: Use a serine residue for catalysis (e.g., trypsin, chymotrypsin).
Cysteine (Thiol) Proteases: Use a cysteine residue's thiol group (e.g., papain, caspases).
Aspartic Proteases: Use two aspartic acid residues to activate a water molecule (e.g., pepsin, renin).
Metalloproteases: Require a metal ion, typically zinc, for their catalytic activity (e.g., carboxypeptidase A, thermolysin).
Threonine Proteases: Use a threonine residue as the catalytic nucleophile.
3. Can you provide an example of how protease works in the human body?
A classic example is the role of pepsin in the stomach. When you eat protein-rich food, the stomach glands secrete pepsin. In the highly acidic environment of the stomach, pepsin acts as an endopeptidase, breaking down large, complex protein molecules into smaller, more manageable polypeptides. This is the first and a vital step in protein digestion.
4. What is the general mechanism of action for a protease enzyme?
The general mechanism involves the protease binding to a specific protein substrate at its active site. A key amino acid residue (like serine or cysteine) or a coordinated water molecule acts as a nucleophile, attacking the carbonyl carbon of a peptide bond. This leads to the formation of an unstable intermediate, which is then hydrolysed by a water molecule, breaking the peptide bond and releasing the resulting fragments. The enzyme is then regenerated to catalyse another reaction.
5. Why don't digestive proteases like trypsin destroy the pancreatic cells that produce them?
This is a critical biological safety measure. Proteases are synthesised and secreted in an inactive form called a zymogen or proenzyme (e.g., trypsinogen for trypsin). These inactive precursors are only activated in the specific location where they are needed, such as the small intestine. This prevents them from destroying the essential proteins within the cells of the pancreas where they are made. This mechanism ensures that powerful digestive enzymes only become active when they have reached their intended target.
6. What is the difference between an endopeptidase and an exopeptidase?
The key difference lies in where they cleave the protein chain.
Endopeptidases (like trypsin and pepsin) act on peptide bonds within the protein chain, breaking large proteins into smaller fragments.
Exopeptidases (like carboxypeptidase) act on peptide bonds at the ends of the protein chain, removing one amino acid at a time from either the carboxyl (C-terminal) or amino (N-terminal) end.
7. What are protease inhibitors and why are they medically important?
Protease inhibitors are molecules that bind to proteases and block their activity. They are critically important in medicine as drugs. For instance, HIV protease inhibitors are a key class of antiretroviral drugs. They work by blocking a specific viral protease that HIV needs to produce mature, infectious virus particles. By inhibiting this enzyme, the drugs prevent the virus from replicating, helping to manage the infection.
8. Beyond digestion, what are some other important functions of proteases in living organisms?
While digestion is a well-known function, proteases are vital for many other cellular and physiological processes:
Blood Coagulation: The serine protease thrombin is essential to the blood clotting cascade, helping to form a clot at a wound site.
Immune Response: They help in destroying foreign pathogens and are involved in regulating the inflammatory response.
Apoptosis: Proteases called caspases play a key role in orchestrating programmed cell death, a process vital for development and tissue maintenance.
Protein Turnover: They help recycle old or damaged proteins within the cell, maintaining cellular health and function.
