Erepsin is a mixture of

enzyme Enzymes () are proteins that act as biological catalysts by accelerating chemical reactions. The molecules upon which enzymes may act are called substrates, and the enzyme converts the substrates into different molecules known as products ...

s contained in a protein fraction found in the intestinal juices that digest peptones into amino acids. It is produced and secreted by the

intestinal gland In histology, an intestinal gland (also crypt of Lieberkühn and intestinal crypt) is a gland found in between villi in the intestinal epithelium lining of the small intestine and large intestine (or colon). The glands and intestinal villi are co ...

s in the

ileum The ileum () is the final 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 posterior intestine or distal intestine m ...

and the

pancreas The pancreas is an organ of the digestive system and endocrine system of vertebrates. In humans, it is located in the abdomen behind the stomach and functions as a gland. The pancreas is a mixed or heterocrine gland, i.e. it has both an en ...

, but it is also found widely in other cells. It is, however, a term now rarely used in scientific literature as more precise terms are preferred.

History

Erepsin was discovered at the beginning of the twentieth century by German physiologist Otto Cohnheim (1873-1953) who found a substance that breaks down peptones into amino acid in the intestines. He termed this hypothetical protease in his protein extract "erepsin" in 1901, derived from a Greek word meaning "I break down" (έρείπω). His discovery was significant as it overturned the previous "hypothesis of resynthesis" which proposed that proteins get broken down into peptones from which proteins may then be resynthesized, and helped establish the idea of free amino acids instead of peptones being the building blocks of protein. Erepsin was originally thought to be a single enzyme or a mixture of a few enzymes involved in the terminal stages of the breakdown of peptides to free amino acids in the intestines. However, it became clear later that erepsin is in fact a complex mixture of different peptidases. It was also found not to be unique to intestinal mucosa and is present widely in many other cells and organisms. The term erepsin fell from use in scientific literature in the latter half of the twentieth century as scientists considered its use as a term for a single enzyme or a few enzymes misleading, and more precise terms such as

aminopeptidase Aminopeptidases are enzymes that catalyze the cleavage of amino acids from the amino terminus ( N-terminus) of proteins or peptides (exopeptidases). They are widely distributed throughout the animal and plant kingdoms and are found in many subcel ...

, carboxypeptidase and

dipeptidase Dipeptidases are enzymes secreted by enterocytes into the small intestine. Dipeptidases hydrolyze bound pairs of amino acids, called dipeptides. Dipeptidases are secreted onto the brush border of the villi in the small intestine, where they cleave ...

are preferred. The term is now considered obsolete.

Properties

Erepsin may contain dipeptidases,

aminopeptidases Aminopeptidases are enzymes that catalyze the cleavage of amino acids from the amino terminus (N-terminus) of proteins or peptides (exopeptidases). They are widely distributed throughout the animal and plant kingdoms and are found in many subcell ...

, occasionally

carboxypeptidases A carboxypeptidase ( EC number 3.4.16 - 3.4.18) is a protease enzyme that hydrolyzes (cleaves) a peptide bond at the carboxy-terminal (C-terminal) end of a protein or peptide. This is in contrast to an aminopeptidases, which cleave peptide bonds at ...

, and others including

leucyl aminopeptidase Leucyl aminopeptidases (, ''leucine aminopeptidase'', ''LAPs'', ''leucyl peptidase'', ''peptidase S'', ''cytosol aminopeptidase'', ''cathepsin III'', ''L-leucine aminopeptidase'', ''leucinaminopeptidase'', ''leucinamide aminopeptidase'', ''FTBL pr ...

prolinase Cytosolic non-specific dipeptidase () also known as carnosine dipeptidase 2 is an enzyme that in humans is encoded by the ''CNDP2'' gene. This enzyme catalyses the following chemical reaction : Hydrolysis of dipeptides, preferentially hydrophobi ...

and

prolidase Xaa-Pro dipeptidase, also known as prolidase, is an enzyme that in humans is encoded by the ''PEPD'' gene. Function Xaa-Pro dipeptidase is a cytosolic dipeptidase that hydrolyzes dipeptides with proline or hydroxyproline at the carboxy termin ...

. It is often grouped under

exopeptidase An exopeptidase is any peptidase that catalyzes the cleavage of the terminal (or the penultimate) peptide bond; the process releases a single amino acid, dipeptide or a tripeptide from the peptide chain. Depending on whether the amino acid is rel ...

s, proteases that work only on the outermost peptide bonds of a polypeptide chain. The optimum pH for the group of enzymes is around pH 8, but some individual enzymes within this group may be distinguished by their differences in stability and optimum pH.

References

{{reflist Enzymes