Chymosin or rennin is an enzyme

Enzyme

Enzymes are proteins that catalyze chemical reactions. In enzymatic reactions, the molecules at the beginning of the process, called substrates, are converted into different molecules, called products. Almost all chemical reactions in a biological cell need enzymes in order to occur at rates...

 found in rennet

Rennet

Rennet is a complex of enzymes produced in any mammalian stomach to digest the mother's milk, and is often used in the production of cheese. Rennet contains many enzymes, including a proteolytic enzyme that coagulates the milk, causing it to separate into solids and liquid...

. It is produced by cows in the lining of the abomasum

Abomasum

The abomasum, also known as the maw, and the rennet-bag, and the read, is the fourth and final stomach compartment in ruminants. It secretes rennin - the artificial form of which is called rennet, and is used in cheese creation....

 (the fourth and final, chamber of the stomach). Chymosin is produced by gastric chief cell

Gastric chief cell

A gastric chief cell is a cell in the stomach that releases pepsinogen, gastric lipase and Chymosin...

s in infants to curdle the milk they ingest, allowing a longer residence in the bowels and better absorption.
Bovine chymosin is now produced recombinantly

Recombinant DNA

Recombinant DNA molecules are DNA sequences that result from the use of laboratory methods to bring together genetic material from multiple sources, creating sequences that would not otherwise be found in biological organisms...

 in , Aspergillus niger var awamori

Aspergillus niger

Aspergillus niger is a fungus and one of the most common species of the genus Aspergillus. It causes a disease called black mold on certain fruits and vegetables such as grapes, onions, and peanuts, and is a common contaminant of food...

, and as alternative resource. The gene is found in humans (on chromosome 1

Chromosome 1 (human)

Chromosome 1 is the designation for the largest human chromosome. Humans have two copies of chromosome 1, as they do with all of the autosomes, which are the non-sex chromosomes. Chromosome 1 spans about 247 million nucleotide base pairs, which are the basic units of information for DNA...

), but it is not expressed

Gene expression

Gene expression is the process by which information from a gene is used in the synthesis of a functional gene product. These products are often proteins, but in non-protein coding genes such as ribosomal RNA , transfer RNA or small nuclear RNA genes, the product is a functional RNA...

.

Enzymatic reaction

Chymosin causes cleavage

Bond cleavage

Bond cleavage, or scission, is the splitting of chemical bonds.If the two electrons in a cleaved covalent bond are divided between the products, the process is known as homolytic fission and free redicals are generated by homolytic cleavage the process is known as homolytic fission or homolysis...

 of a specific linkage — the peptide bond

Peptide bond

This article is about the peptide link found within biological molecules, such as proteins. A similar article for synthetic molecules is being created...

 between 105 and 106, phenylalanine

Phenylalanine

Phenylalanine is an α-amino acid with the formula C6H5CH2CHCOOH. This essential amino acid is classified as nonpolar because of the hydrophobic nature of the benzyl side chain. L-Phenylalanine is an electrically neutral amino acid, one of the twenty common amino acids used to biochemically form...

 and methionine

Methionine

Methionine is an α-amino acid with the chemical formula HO2CCHCH2CH2SCH3. This essential amino acid is classified as nonpolar. This amino-acid is coded by the codon AUG, also known as the initiation codon, since it indicates mRNA's coding region where translation into protein...

, in K-Casein

K-Casein

K-Casein is a mammalian milk protein involved in a number of important physiological processes. In the gut, the ingested protein is split into an insoluble peptide and a soluble hydrophilic glycopeptide...

, the native substrate of this enzyme. Proceeding the uneven cleavage of kappa-casein, the opposite charges on the substrate can interact with the enzyme; histidines on the kappa-casein are attracted to glutamates and aspartate on chymosin. When chymosin is not binding substrate, a beta-hairpin, sometimes referred to as "the flap," can hydrogen bond with the active site, therefore covering it and not allowing further binding of substrate.
If this reaction applies to milk, the specific linkage between the hydrophobic (para-casein) and hydrophilic (acidic glycopeptide

Glycopeptide

Glycopeptides are peptides that contain carbohydrate moieties covalently attached to the side chains of the amino acid residues that constitute the peptide. Over the past few decades it has been recognised that glycans on cell surface and those bound to proteins play a critical role in biology...

) group of casein

Casein

Casein is the name for a family of related phosphoprotein proteins . These proteins are commonly found in mammalian milk, making up 80% of the proteins in cow milk and between 60% and 65% of the proteins in human milk....

 inside milk would be broken, since they are joined by phenylalanine and methionine. The hydrophobic group would unite and would form a 3D

Three-dimensional space

Three-dimensional space is a geometric 3-parameters model of the physical universe in which we live. These three dimensions are commonly called length, width, and depth , although any three directions can be chosen, provided that they do not lie in the same plane.In physics and mathematics, a...

 network to trap the aqueous phase of the milk. The resultant product is calcium phosphocaseinate. Due to this reaction, rennin is used to bring about the extensive precipitation

Precipitation (chemistry)

Precipitation is the formation of a solid in a solution or inside anothersolid during a chemical reaction or by diffusion in a solid. When the reaction occurs in a liquid, the solid formed is called the precipitate, or when compacted by a centrifuge, a pellet. The liquid remaining above the solid...

 and curd

Curd

Curds are a dairy product obtained by curdling milk with rennet or an edible acidic substance such as lemon juice or vinegar, and then draining off the liquid portion. The increased acidity causes the milk proteins to tangle into solid masses, or curds. The remaining liquid, which contains only...

 formation in cheese

Cheese

Cheese is a generic term for a diverse group of milk-based food products. Cheese is produced throughout the world in wide-ranging flavors, textures, and forms....

 making.

Examples

Listed below are the cow Cym gene and corresponding human pseudogene:

Further reading

•  

External links

• The MEROPS
  Merops
  Merops may refer to:* Merops , a genus of bee-eaters.* MEROPS, an on-line database for peptidases.It may also refer to several figures from Greek mythology:* King of Ethiopia, husband of Clymene, who lay with Helios and bore Phaethon...
  
  online database for peptidases and their inhibitors: A01.006