Enzymes that digest proteins

Enzymes that digest proteins

Enzymes that hydrolyze peptide bonds to break down proteins into smaller peptides or amino acids are called proteases, often referred to as proteolytic enzymes or proteinases. These enzymes are essential for many biological activities, such as protein turnover, cellular control, and digestion. Proteases come in several varieties, and they are categorized according to where they work and how they work. Proteases that are important in the digestion of proteins include:


One enzyme that is essential to the stomach’s process of breaking down proteins is called pepsin. It is created and secreted as pepsinogen, an inactive precursor, by the gastric main cells in the lining of the stomach. The stomach’s acidic environment then converts pepsinogen into its active form.

Here are some key points about pepsin:

Activation: After being secreted into the stomach, pepsinogen comes into contact with the hydrochloric acid (HCl)-induced acidic environment. By eliminating a section of the molecule, this acidic environment causes pepsinogen to change into its active form, pepsin.

Ideal pH: Pepsin functions best in a very acidic environment (pH between 1.5 and 2.0). The stomach’s acidic environment contributes to pepsin’s continued functioning.

Substrate Specificity: Proteins may be broken down by pepsin into smaller peptides with great efficiency. Certain amino acid peptide bonds are broken by it, causing proteins to hydrolyze into shorter polypeptide chains.

Function in Protein Digestion: Pepsin is essential for the first stages of the digestion of food proteins in the stomach. It reduces proteins to tiny peptides so that other proteases in the small intestine may further break them down.

Protein Activation: As part of a positive feedback loop in the stomach’s protein-digesting action, pepsin also possesses the capacity to activate more pepsinogen molecules.

                   It’s crucial to remember that pepsin mostly functions in the stomach. Once the partially broken down food, or chyme, enters the small intestine, bicarbonate ions neutralize the acidic pH, and pancreatic enzymes like trypsin, chymotrypsin, and carboxypeptidase aid in the remaining protein digestion. When proteins are broken down, tiny peptides and amino acids are produced that the small intestine can absorb.



Trypsin is a member of the class of enzymes known as serine proteases, which are enzymes that break peptide bonds by using a serine residue in their active site. Trypsin is an essential digestive enzyme that reduces big protein molecules into smaller peptides. Trypsin’s salient characteristics are as follows:

Source: The pancreas produces trypsinogen, an inactive precursor of trypsin. After that, it is discharged into the small intestine, where enteropeptidase, another enzyme, acts to activate it.

Activation: Enteropeptidase cleaves a particular peptide link to transform trypsinogen into its active form, trypsin. This activation stage is an essential regulatory mechanism that keeps the pancreas’s trypsin from activating too soon.

Substance Particularity:For peptide bonds on the carboxyl side of the amino acids arginine and lysine, trypsin demonstrates substrate selectivity. Trypsin is distinguished from other proteases by its specificity, such as chymotrypsin, which has a distinct substrate specificity.

Ideal pH: Trypsin works best in a slightly alkaline solution. Its action is limited to a pH range of 7.5 to 8.5. This is in line with its function in the small intestine, which has a pH higher than the stomach’s acidic environment.

Part in the Digestion Process:Trypsin disassembles proteins into smaller peptides by cleaving their peptide links. Together with other pancreatic enzymes like carboxypeptidase and chymotrypsin, it guarantees that food proteins are fully broken down into their component amino acids.

Physiological Function:Beyond its role in digesting, trypsin has a number of physiological roles, such as immunological response, tissue repair, and blood coagulation. It also contributes to the activation of additional digestive enzymes.

                   Trypsin’s activity is strictly controlled to guarantee healthy digestion and shield the body’s own tissues from harm. For food proteins to be broken down into components that the body can absorb and use, trypsin and other proteases must work in unison.


The digestive enzyme chymotrypsin is a member of the serine protease family. It is essential to the small intestine’s process of breaking down proteins. The following are some of chymotrypsin’s main characteristics and uses:

Source: The pancreas produces chymotrypsinogen, an inactive precursor of chymotrypsin. Next, an enzyme known as trypsin activates it in the small intestine.

Activation: A little piece of the molecule is cleaved to produce the active form, chymotrypsin, which is the outcome of activating chymotrypsinogen.

Substrate Specificity: Peptide bonds next to big, hydrophobic amino acids like phenylalanine, tryptophan, and tyrosine are the only ones that chymotrypsin is specialized for. It disassembles proteins into smaller peptides by cleaving these peptide links.

Function: Chymotrypsin aids in the general digestion of food proteins, working in tandem with trypsin and other proteases. It breaks down polypeptides into smaller pieces and ultimately into individual amino acids in concert with trypsin and carboxypeptidase.

Ideal pH: The bicarbonate ions found in the small intestine produce a slightly alkaline pH environment that is conducive to chymotrypsin’s activity.

Restrictors: Certain inhibitors, such as serpins (serine protease inhibitors), can reduce the action of chymotrypsin.

                    Proteins from the diet are broken down into absorbable units—amino acids and small peptides—by the combined action of chymotrypsin, trypsin, carboxypeptidase, and other proteases. This ensures that proteins are efficiently absorbed in the small intestine and subsequently utilized by the body for various physiological processes.


A particular kind of protease enzyme called elastase targets the fibrous protein elastin, which is present in connective tissues including the skin, blood vessels, and lungs. These tissues’ elasticity and tenacity are due to elastin. Elastase aids in the processes of tissue remodeling and healing by breaking down elastin into smaller peptides.

To avoid undue tissue damage, the body closely controls the activity of elastase. Certain illnesses, including as inflammatory disorders and respiratory ailments like chronic obstructive pulmonary disease (COPD), have been linked to imbalances in elastase activity.

In order to control elastase activity and stop tissue damage in specific disorders, researchers have looked at elastase inhibitors as possible therapeutic medicines. Gaining knowledge about the function of elastase is crucial for comprehending tissue physiology, healing, and a variety of pathological situations.


One enzyme that is essential to the breakdown of proteins is carboxypeptidase. It works by cleaving individual amino acids off proteins and peptides at their carboxyl (C-terminal) terminus. This enzyme aids in the breakdown of peptides into their component amino acids, which is especially crucial in the latter stages of protein digestion.

Although there are many distinct types of carboxypeptidases in different tissues and organs, pancreatic carboxypeptidase is one well-known kind. The pancreas secretes pancreatic carboxypeptidase, which is then released into the small intestine where it functions in concert with other digesting enzymes.

The terminal (C-terminal) amino acid’s peptide link with the remainder of the peptide chain is hydrolyzed throughout the process. A free amino acid is released as a result of this process. When peptides are broken down into their constituent amino acids, carboxypeptidase plays a crucial role in allowing the small intestine to receive and use the individual amino acids for physiological purposes.

All things considered, carboxypeptidase is an essential enzyme that aids in the process of dissolving complex protein structures into more easily absorbed and used amino acid components by the body.


The hydrolysis of amino acids from the amino (N)-terminal end of peptides and proteins is catalyzed by enzymes called aminopeptidases. These enzymes are essential for the latter stages of protein digestion because they disassemble peptides into individual amino acids, which the body may absorb through the intestinal mucosa.

Aminopeptidases come in diverse varieties and are distributed throughout the body, especially in the digestive tract. Here are a few noteworthy instances:

Aminopeptidase N (APN): This enzyme, which is located in the small intestine’s brush border membrane, aids in the hydrolysis of amino acids from peptides’ N-termini. It is essential for the breakdown of peptides into absorbable amino acids during the latter stages of protein digestion.

Aminopeptidase P: This enzyme aids in the hydrolysis of N-terminal amino acids from peptides and is likewise found in the brush border membrane of the small intestine.

Leucine aminopeptidase: This enzyme, which is found in the liver, kidneys, and small intestine, cleaves amino acids off peptides’ N-termini, preferring leucine to other amino acids.

                      The gastrointestinal tract’s overall effectiveness in breaking down and absorbing proteins is influenced by the activity of aminopeptidases. Peptides may be easily absorbed by intestinal epithelial cells and sent into the bloodstream for distribution to different bodily tissues once they have been broken down into individual amino acids.

Together, these enzymes aid in the full breakdown of food proteins, producing tiny peptides and amino acids that the small intestine may absorb and use for a variety of physiological processes.

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