Pepsin

Pepsin /ˈpɛpsɪn/ is an <a href="/facts/Endopeptidase/LeEhY5xV">endopeptidase</a> that breaks down <a href="/facts/Protein/Jxmagu3E">proteins</a> into smaller <a href="/facts/Peptide/C4ltc7UG">peptides</a> and <a href="/facts/Amino_acid/WDxYwBny">amino acids</a>. It is one of the main <a href="/facts/Digestive_enzyme/aRYCbJHe">digestive enzymes</a> in the <a href="/facts/Digestion/sjUBmhBS">digestive systems</a> of humans and many other animals, where it helps <a href="/facts/Digestion/sjUBmhBS">digest</a> the proteins in <a href="/facts/Food/RgNq6NAK">food</a>. Pepsin is an <a href="/facts/Aspartic_protease/TSywUn4P">aspartic protease</a>, using a catalytic aspartate in its <a href="/facts/Active_site/u9ua7rGu">active site</a>.
It is one of three principal endopeptidases (enzymes cutting proteins in the middle) in the <a href="/facts/Human_digestive_system/SdpF0sWq">human digestive system</a>, the other two being <a href="/facts/Chymotrypsin/hht9v7eG">chymotrypsin</a> and <a href="/facts/Trypsin/wrwS23rh">trypsin</a>. There are also <a href="/facts/Exopeptidase/4NJldxAv">exopeptidases</a> which remove individual amino acids at both ends of proteins (<a href="/facts/Carboxypeptidase/RmQNzvCR">carboxypeptidases</a> produced by the pancreas and <a href="/facts/Aminopeptidase/IlFXleE4">aminopeptidases</a> secreted by the small intestine). During the process of digestion, these enzymes, each of which is specialized in severing links between particular types of <a href="/facts/Amino_acid/WDxYwBny">amino acids</a>, collaborate to break down dietary proteins into their components, i.e., peptides and amino acids, which can be readily <a href="/facts/Small_intestine/1AQ8RJ4m">absorbed by the small intestine</a>. The cleavage specificity of pepsin is broad, but some <a href="/facts/Amino_acid/WDxYwBny">amino acids</a> like <a href="/facts/Tyrosine/RJhEgE4C">tyrosine</a>, <a href="/facts/Phenylalanine/eyojfW7t">phenylalanine</a> and <a href="/facts/Tryptophan/JcUxlxAh">tryptophan</a> increase the probability of cleavage.
Pepsin's <a href="/facts/Zymogen/Qa9SGXVS">zymogen</a> (proenzyme), pepsinogen, is released by the <a href="/facts/Gastric_chief_cell/Yb3L1QsX">gastric chief cells</a> in the stomach wall, and upon mixing with the <a href="/facts/Hydrochloric_acid/HqItJlUT">hydrochloric acid</a> of the <a href="/facts/Gastric_acid/btVCyhYH">gastric juice</a>, pepsinogen activates to become pepsin.

Pepsin open-in-new

Pepsin