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Pepsin
 
 
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Pepsin is an enzyme
Enzyme

Enzymes are biomolecules that catalysis chemical reactions. Almost all enzymes are proteins. In enzymatic reactions, the molecules at the beginning of the process are called Substrate , and the enzyme converts them into different molecules, the products....
 that is released by the chief cell
Gastric chief cell

A gastric chief cell is a cell in the stomach that releases pepsinogen, gastric lipase and rennin. The cell stains basophilic upon H&E stain due to the large proportion of rough endoplasmic reticulum in its cytoplasm....
s in the stomach
Stomach

In most mammals, the stomach is a hollow muscular organ of the gastrointestinal tract involved in the second phase of digestion, following mastication....
 and which degrades food protein
Protein

Proteins are organic compounds made of amino acids arranged in a linear chain and joined together by peptide bonds between the carboxyl and amino groups of adjacent amino acid Residue ....
s into peptides. Pepsin was discovered in 1836 by Theodor Schwann
Theodor Schwann

----Theodor Schwann was a Germany zoologist. His many contributions to biology include the development of cell theory, the discovery of Schwann cells in the peripheral nervous system, the discovery and study of pepsin, the discovery of the organic nature of yeast, and the invention of the term metabolism....
 who also coined this enzyme's name from the Greek
Greek language

Greek is an Indo-European languages native to the southern Balkan peninsula, the language of the Greek people. It forms an independent branch within Indo-European....
 word pepsis, meaning digestion
Digestion

Digestion is the mechanical and chemical breaking down of food into smaller components, to a form that can be Absorption, for instance, by a blood stream....
 (peptein: to digest). It was the first animal enzyme to be discovered, and in 1929 it became one of the first enzymes to be crystallized, by John H. Northrop. Pepsin is a digestive protease
Protease

A protease is any enzyme that conducts proteolysis, that is, begins protein catabolism by hydrolysis of the peptide bonds that link amino acids together in the polypeptide chain, which form a molecule of protein....
.

Precursor
Pepsin is expressed
Protein expression

Protein expression is a subcomponent of gene expression. It consists of the stages after DNA has been translated into amino acid chains, which are ultimately folded into proteins....
 as a pro-form zymogen
Zymogen

A zymogen is an inactive enzyme Protein precursor. A zymogen requires a biochemical change for it to become an active enzyme. The biochemical change usually occurs in a lysosome where a specific part of the precursor enzyme is cleaved in order to activate it....
, pepsinogen, whose primary structure
Primary structure

In biochemistry, the primary structure of a biological molecule is the exact specification of its atomic composition and the chemical bonds connecting those atoms ....
  has an additional 44 amino acids
Amino acid

In chemistry, an amino acid is a molecule containing both amine and carboxyl functional groups. These molecules are particularly important in biochemistry, where this term refers to alpha-amino acids with the general formula H2NCHRCOOH, where R is an organic substituent....
.

In the stomach, chief cell
Chief cell

In general, a chief cell is a cell which releases a precursor enzyme. There are two types of chief cells which are most commonly referenced:* A gastric chief cell is a cell in the stomach that releases pepsinogen and rennin....
s release pepsinogen.






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Encyclopedia


Pepsin is an enzyme
Enzyme

Enzymes are biomolecules that catalysis chemical reactions. Almost all enzymes are proteins. In enzymatic reactions, the molecules at the beginning of the process are called Substrate , and the enzyme converts them into different molecules, the products....
 that is released by the chief cell
Gastric chief cell

A gastric chief cell is a cell in the stomach that releases pepsinogen, gastric lipase and rennin. The cell stains basophilic upon H&E stain due to the large proportion of rough endoplasmic reticulum in its cytoplasm....
s in the stomach
Stomach

In most mammals, the stomach is a hollow muscular organ of the gastrointestinal tract involved in the second phase of digestion, following mastication....
 and which degrades food protein
Protein

Proteins are organic compounds made of amino acids arranged in a linear chain and joined together by peptide bonds between the carboxyl and amino groups of adjacent amino acid Residue ....
s into peptides. Pepsin was discovered in 1836 by Theodor Schwann
Theodor Schwann

----Theodor Schwann was a Germany zoologist. His many contributions to biology include the development of cell theory, the discovery of Schwann cells in the peripheral nervous system, the discovery and study of pepsin, the discovery of the organic nature of yeast, and the invention of the term metabolism....
 who also coined this enzyme's name from the Greek
Greek language

Greek is an Indo-European languages native to the southern Balkan peninsula, the language of the Greek people. It forms an independent branch within Indo-European....
 word pepsis, meaning digestion
Digestion

Digestion is the mechanical and chemical breaking down of food into smaller components, to a form that can be Absorption, for instance, by a blood stream....
 (peptein: to digest). It was the first animal enzyme to be discovered, and in 1929 it became one of the first enzymes to be crystallized, by John H. Northrop. Pepsin is a digestive protease
Protease

A protease is any enzyme that conducts proteolysis, that is, begins protein catabolism by hydrolysis of the peptide bonds that link amino acids together in the polypeptide chain, which form a molecule of protein....
.

Precursor


Pepsin is expressed
Protein expression

Protein expression is a subcomponent of gene expression. It consists of the stages after DNA has been translated into amino acid chains, which are ultimately folded into proteins....
 as a pro-form zymogen
Zymogen

A zymogen is an inactive enzyme Protein precursor. A zymogen requires a biochemical change for it to become an active enzyme. The biochemical change usually occurs in a lysosome where a specific part of the precursor enzyme is cleaved in order to activate it....
, pepsinogen, whose primary structure
Primary structure

In biochemistry, the primary structure of a biological molecule is the exact specification of its atomic composition and the chemical bonds connecting those atoms ....
  has an additional 44 amino acids
Amino acid

In chemistry, an amino acid is a molecule containing both amine and carboxyl functional groups. These molecules are particularly important in biochemistry, where this term refers to alpha-amino acids with the general formula H2NCHRCOOH, where R is an organic substituent....
.

In the stomach, chief cell
Chief cell

In general, a chief cell is a cell which releases a precursor enzyme. There are two types of chief cells which are most commonly referenced:* A gastric chief cell is a cell in the stomach that releases pepsinogen and rennin....
s release pepsinogen. This zymogen is activated by hydrochloric acid
Hydrochloric acid

Hydrochloric acid is the solution of hydrogen chloride in water. It is a highly corrosive, strong acid mineral acid and has major industrial uses....
 (HCl), which is released from parietal cell
Parietal cell

Parietal cells, or oxyntic cells, are the stomach epithelium cell s that secrete gastric acid and intrinsic factor....
s in the stomach lining. The hormone gastrin
Gastrin

In humans, gastrin is a hormone that stimulates secretion of gastric acid by the parietal cells of the stomach and aids in gastric motility. It is released by G cells in the stomach, duodenum, and the pancreas....
 and the vagus nerve
Vagus nerve

The vagus nerve is the tenth of twelve paired cranial nerves, and is the only nerve that starts in the brainstem and extends, through the jugular foramen, down below the head , to the neck, chest and abdomen, where it contributes to the innervation of the viscera....
 trigger the release of both pepsinogen and HCl from the stomach lining when food is ingested. Hydrochloric acid creates an acidic environment which allows pepsinogen to unfold and cleave itself in an autocatalytic fashion, thereby generating pepsin (the active form). Pepsin cleaves the 44 amino acids from pepsinogen to create more pepsin. Pepsin will digest up to 20% of ingested carbon bonds by cleaving preferentially after the N-terminal of aromatic amino acids such as phenylalanine
Phenylalanine

Phenylalanine is an a-amino acid with the chemical formula HO2CCHCH2C6H5, which is found naturally in the breast milk of mammals and manufactured for food and drink products and are also sold as nutritional supplements for their reputed analgesic and antidepressant effects....
, tryptophan
Tryptophan

Tryptophan is one of the 20 List of standard amino acids, as well as an essential amino acid in the human diet. It is encoded in the standard genetic code as the codon UGG....
, and tyrosine
Tyrosine

Tyrosine or 4-hydroxyphenylalanine, is one of the 20 amino acids that are used by cell to protein biosynthesis proteins. This is a non-essential amino acid and it is found in casein....
. Peptides may be further digested by other proteases (in the duodenum
Duodenum

The duodenum is the first section of the small intestine in most higher vertebrates, including mammals, reptiles, and birds. In fish, the divisions of the small intestine are not as clear and the terms anterior intestine or proximal intestine may be used instead of duodenum....
) and eventually absorbed by the body. Pepsin is stored as pepsinogen so it will only be released when needed, and does not digest the body's own proteins in the stomach's lining.

Pepsin functions best in acidic environments and is often found in an acidic environment, particularly those with a pH of 1.5 to 2. Pepsin denatures if the pH is more than 5.0.

Pepsin is said to have an optimum temperature between 37°C and 42°C in humans.

Pepsin is potently inhibited by the peptide inhibitor pepstatin
Pepstatin

Pepstatin is a potent inhibitor of aspartyl proteases. It is a hexa-peptide containing the unusual amino acid statine , having the sequence Iva-Val-Val-Sta-Ala-Sta....
.

Storage


Pepsins should be stored at very cold temperatures (between -20°C and -80°C) to prevent autolysis (self-cleavage). Autolysis may also be prevented by storage of pepsins at pH 11 or by using pepsins modified by e.g. reductive methylation. When the pH is adjusted back to pH 6 activity returns.

See also


  • Trypsin
    Trypsin

    Trypsin is a serine protease found in the digestive system, where it breaks down proteins. Trypsin predominantly cleaves peptide chains at the carboxyl side of the amino acids lysine and arginine, except when either is followed by proline....
  • Chymotrypsin
    Chymotrypsin

    Chymotrypsin is a digestive enzyme that can perform proteolysis. Chymotrypsin cleaves peptides at the carboxyl side of tyrosine, tryptophan, and phenylalanine because these three amino acids contain aromatic rings, which fit into a 'hydrophobic pocket' in the enzyme....


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