How Pepsin Works and Why It’s Vital for Biology Students
The human digestive system is a fascinating set of digestive organs and enzymes working together. These organs along with important enzymes work together to help absorb and assimilate the food that we eat efficiently. Pepsin is concerned with breaking down different proteins in our food. The protein in our food is converted into amino acids and peptides by pepsin along with two other principal proteases of our body namely chymotrypsin and trypsin.
This enzyme was first discovered in 1936 by Theodore Schwann. Pepsin was named so after the Greek word Pepsis which literally means digestion. Refer to the official website of Vedantu or download the app for an elaborate and comprehensive explanation.
In the following article you will learn in detail about the following:
Pepsin
Sources of Pepsin
Structure of Pepsin
Characteristics of Pepsin
Classification of Pepsin
Working Mechanism of pepsin
Applications of Pepsin.
What is Pepsin?
Pepsin is an endopeptidase enzyme that degrades proteins into peptides. It is formed in the chief cells of the stomach lining and is one of the most important digestive enzymes in humans and many other animals' digestive systems, where it aids in the digestion of proteins. Pepsin is an aspartic protease with an active site that contains a catalytic aspartate.
Where is Pepsin found?
Pepsin enzymes are found in the stomach. Pepsin is a stomach enzyme that aids in the digestion of proteins in food. Pepsin is secreted by gastric chief cells as pepsinogen, an inactive zymogen. Hydrochloric acid is secreted by parietal cells in the stomach lining, which lowers the pH of the stomach. Pepsin is activated by a low pH (1.5 to 2).
Structure of Pepsin
Pepsin is a monomer (chain protein) made up of two folding domains that are separated by a deep cleft. Pepsin's catalytic site is formed at the domain junction, with two aspartic acid residues, Asp32 and Asp215, in each domain. The water molecule aids pepsin's catalysis by allowing the active carboxyl group to bear positive and negative charges with aspartic acid 215 and 32, respectively, breaking the peptide bond in the protein.
Activity and Stability of Pepsin
In acidic environments with a pH of 1.5 to 2.5, pepsin is most active. Pepsin works best at temperatures between 37 and 42 degrees Celsius. As a result, the stomach is the main site of synthesis and function (pH 1.5 to 2).
In humans, pepsin concentrations in the stomach range from 0.5 to 1 mg/mL. At pH 6.5 and above, pepsin is inactive, but it is not completely denatured or irreversibly inactivated until pH 8.0. As a result, re-acidification will reactivate pepsin in solutions up to pH 8.0. The safety of pepsin at high pH has important consequences for laryngopharyngeal reflux disease.
Following a gastric reflux case, pepsin persists in the larynx. Pepsin will be inactive at the mean pH of the laryngopharynx (pH = 6.8), but it may be reactivated during subsequent acid reflux events, causing damage to local tissues. Pepsin has a wide range of cleavage specificity.
Working of Pepsin Enzyme
Pepsin is expressed as a zymogen called pepsinogen, which has an additional 44 amino acids in its primary structure than the active enzyme.
Pepsinogen is generated by chief cells in the stomach. Hydrochloric acid (HCl), which is released from parietal cells in the stomach lining, activates this zymogen. When food is consumed, the hormone gastrin and the vagus nerve trigger the release of pepsinogen and HCl from the stomach lining.
The acidic environment produced by hydrochloric acid allows pepsinogen to unfold and cleave itself in an autocatalytic manner, resulting in the development of pepsin (the active form). To make more pepsin, pepsin cleaves the 44 amino acids in pepsinogen.
Classification of Pepsinogen
Pepsinogens are divided into five categories based on their primary structure: pepsinogen A (also known as pepsinogen I), pepsinogen B, progastricsin (also known as pepsinogen II and pepsinogen C), prochymosin (also known as prorennin), and pepsinogen F. (also called pregnancy-associated glycoprotein).
What Does Pepsin Do?
Pepsin is a proteolytic enzyme released by chief cells, which are specialized in the stomach. It is a component of gastric juice that aids in food digestion. Pepsin is a digestive enzyme that breaks down large polypeptides into smaller peptide fragments in the stomach's acidic environment (pH 1.5-2.5).
Pepsin preferentially hydrolyzes peptide bonds containing the aromatic amino acids' amine group (tryptophan, phenylalanine, and tyrosine). Pepsin is a stomach enzyme that aids in the digestion of proteins in food. Pepsin is secreted by gastric chief cells as pepsinogen, an inactive zymogen. Hydrochloric acid is secreted by parietal cells in the stomach lining, which lowers the pH of the stomach.
The function of pepsin in the stomach is to break down proteins in foods like meat and eggs into smaller pieces (polypeptides). It just breaks down proteins at specific stages, so the protein isn't fully digested to the amino acid level.
Applications of Pepsin
Pepsin can be used in the food industry.
Pepsin is found in pancreatic curd that condenses and twists during the processing of cheese.
Pepsin may be used to add whipping qualities to soybean protein and gelatin.
It can also turn pre-cooked cereals into instant hot cereals and change the plant protein used in non-dairy snacks.
Pepsin can also be used to make protein hydrolysates from animal and plant sources for seasoning food and beverages.
It is used in the leather industry to extract hair and residual tissue from leather, as well as to retrieve silver from the abandoned photographic film by digesting the gelatin layer that stores the silver.
Historically, it has also been used as medicine in the form of laxatives when combined with Senna. The first Pepsin syrup was sold in the 1800s. It is also used in Dr Pepper's pepsin Bitters.
It is used in medical research.
As can be seen, pepsin is a complicated enzyme with several uses in our digestive system. It is crucial for the healthy functioning of our digestive systems. Pepsin has a complicated structure and it has been classified into several subcategories. One must note that the role of pepsin is not only limited to digesting proteins in our food. The latest research shows that the functions of Pepsin are far more elaborate than was previously thought. Research shows that it also aids in the proper functioning of our immune system by digestive Nuclein acids. These acids are essential components of DNA and RNA.
Therefore it is essential to understand the working of the enzyme Pepsin as it is a fascinating enzyme with several crucial functions required for human life.
FAQs on Pepsin: Key Enzyme in Digestion
1. What is pepsin and what is its primary function in the human body?
Pepsin is a crucial digestive enzyme found in the stomach. Its primary function is to act as a protease, which means it initiates the digestion of proteins from the food we eat. It breaks down large, complex protein molecules into smaller fragments called peptones and proteoses, preparing them for further digestion in the small intestine.
2. Where is pepsin produced and activated in the digestive system?
Pepsin is produced in an inactive form called pepsinogen by the chief cells located in the lining of the stomach. Activation occurs within the stomach's acidic environment when pepsinogen comes into contact with hydrochloric acid (HCl), which is secreted by the parietal cells. The HCl converts pepsinogen into the active enzyme, pepsin.
3. Why is it necessary for pepsin to be secreted in an inactive form?
Pepsin is a powerful protein-digesting enzyme. If it were produced in its active form inside the chief cells, it would digest the very cells that create it, leading to a process called autodigestion and damaging the stomach lining. Secreting it as inactive pepsinogen ensures that it only becomes active in the protective environment of the stomach cavity, where a thick mucus layer prevents it from harming the stomach wall.
4. What is the ideal pH for pepsin to function, and why is this significant?
The ideal pH for pepsin to function effectively is highly acidic, typically between 1.5 and 2.5. This is significant because the stomach naturally maintains this low pH level due to the presence of hydrochloric acid. This acidic environment is essential for two reasons: it helps to activate pepsinogen into pepsin, and it provides the optimal conditions for the active pepsin enzyme to break down proteins efficiently.
5. What types of food does the enzyme pepsin help to digest?
Pepsin specifically acts on proteins. It begins the digestive process for proteins found in a wide variety of foods, including:
- Meat, poultry, and fish
- Eggs
- Dairy products like milk and cheese
- Legumes and beans
- Nuts and seeds
6. How does pepsin differ from another major protein-digesting enzyme, trypsin?
While both are proteases, pepsin and trypsin differ in several key ways:
- Operating Environment: Pepsin functions in the highly acidic environment of the stomach (pH 1.5-2.5), whereas trypsin functions in the alkaline environment of the small intestine (pH around 8.0).
- Source: Pepsin is secreted by the stomach lining, while trypsin is produced by the pancreas and secreted into the small intestine.
- Activation: Pepsin is activated by hydrochloric acid (HCl), while trypsin is activated from its precursor, trypsinogen, by an enzyme called enterokinase.
7. What happens to pepsin when it moves from the stomach to the small intestine?
When the acidic contents of the stomach, including pepsin, move into the small intestine, they are mixed with alkaline secretions like bicarbonate from the pancreas. This rapidly neutralises the acid and raises the pH. In this new alkaline environment, pepsin becomes denatured; it loses its specific three-dimensional structure and is permanently inactivated. It can no longer function as an enzyme.
