| pepsin B | |||||||||
|---|---|---|---|---|---|---|---|---|---|
| Identifiers | |||||||||
| EC no. | 3.4.23.2 | ||||||||
| CAS no. | 9025-48-3 | ||||||||
| Databases | |||||||||
| IntEnz | IntEnz view | ||||||||
| BRENDA | BRENDA entry | ||||||||
| ExPASy | NiceZyme view | ||||||||
| KEGG | KEGG entry | ||||||||
| MetaCyc | metabolic pathway | ||||||||
| PRIAM | profile | ||||||||
| PDB structures | RCSB PDB PDBe PDBsum | ||||||||
| |||||||||
| pepsin C (gastricsin) | |||||||||
|---|---|---|---|---|---|---|---|---|---|
| Identifiers | |||||||||
| EC no. | 3.4.23.3 | ||||||||
| CAS no. | 9012-71-9 | ||||||||
| Databases | |||||||||
| IntEnz | IntEnz view | ||||||||
| BRENDA | BRENDA entry | ||||||||
| ExPASy | NiceZyme view | ||||||||
| KEGG | KEGG entry | ||||||||
| MetaCyc | metabolic pathway | ||||||||
| PRIAM | profile | ||||||||
| PDB structures | RCSB PDB PDBe PDBsum | ||||||||
| |||||||||
Pepsin /ˈpɛpsɪn/ is an endopeptidase that breaks down proteins into smaller peptides and amino acids. It is one of the main digestive enzymes in the digestive systems of humans and many other animals, where it helps digest the proteins in food. Pepsin is an aspartic protease, using a catalytic aspartate in its active site.[2]
It is one of three principal endopeptidases (enzymes cutting proteins in the middle) in the human digestive system, the other two being chymotrypsin and trypsin. There are also exopeptidases which remove individual amino acids at both ends of proteins (carboxypeptidases produced by the pancreas and aminopeptidases secreted by the small intestine). During the process of digestion, these enzymes, each of which is specialized in severing links between particular types of amino acids, collaborate to break down dietary proteins into their components, i.e., peptides and amino acids, which can be readily absorbed by the small intestine. The cleavage specificity of pepsin is broad, but some amino acids like tyrosine, phenylalanine and tryptophan increase the probability of cleavage.[3]
Pepsin's zymogen (proenzyme), pepsinogen, is released by the gastric chief cells in the stomach wall, and upon mixing with the hydrochloric acid of the gastric juice, pepsinogen activates to become pepsin.[2]
- ^ PDB: 1PSO; Fujinaga M, Chernaia MM, Tarasova NI, Mosimann SC, James MN (May 1995). "Crystal structure of human pepsin and its complex with pepstatin". Protein Science. 4 (5): 960–72. doi:10.1002/pro.5560040516. PMC 2143119. PMID 7663352.
- ^ a b "Enzyme entry 3.4.23.1". ExPASy Bioinformatics Resource Portal. SIB. Retrieved 14 Dec 2008.
- ^ Hamuro Y, Coales SJ, Molnar KS, Tuske SJ, Morrow JA (April 2008). "Specificity of immobilized porcine pepsin in H/D exchange compatible conditions". Rapid Communications in Mass Spectrometry. 22 (7): 1041–6. Bibcode:2008RCMS...22.1041H. doi:10.1002/rcm.3467. PMID 18327892.