Chymosin
Identifiers
EC number	3.4.23.4
CAS number	9001-98-3
IntEnz	IntEnz view
BRENDA	BRENDA entry
ExPASy	NiceZyme view
KEGG	KEGG entry
MetaCyc	metabolic pathway
PRIAM	profile
PDB	structures
Gene Ontology	AmiGO / EGO
Search PMC articles PubMed articles

Chymosin (or rennin(pronounced /ˈreːnɨn/ REH-nin), not to be confused with renin, a kidney hormone) is an aspartic acid protease enzyme found in rennet. It is produced by the cow, in the lining of the abomasum (the fourth, final, chamber of its stomach). Bovine chymosin is produced nowadays recombinantly in E. coli, Aspergillus niger var awamori, and K. lactis as alternative resource to the one from the cows. The gene is found in humans (on chromosome 1), but it is not in a functioning form. Rennin is produced by gastric chief cells in infants to curdle the milk they ingest, allowing a longer residence in the bowels and better absorption.

[edit] Enzymatic reaction

Chymosin causes cleavage of a specific linkage — the peptide bond between phenylalanine and methionine in the K-Casein. If this reaction applies to milk, the specific linkage between the hydrophobic (para-casein) and hydrophilic (acidic glycopeptide) group of casein inside milk would be broken, since they are joined by phenylalanine and methionine. The hydrophobic group would unite together and would form a 3D 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 and curd formation in cheese making.

[edit] Examples

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

Chymosin [Precursor] (B.taurus or C.dromedarius) Identifiers Symbol Cym Alt. symbols CPC Entrez 529879 PDB 4CMS RefSeq NP_851337.1 UniProt Q9GK11 Other data

chymosin pseudogene (H.sapiens) Identifiers Symbol CYMP Entrez 643160 HUGO 2588 OMIM 118943 RefSeq NR_003599 Other data Locus Chr. 1 p13.3

[edit] References