Pepsin (EC 3.4.23.1)

Pepsin from pig stomach. Its inactive precursor is the pepsinogen secreted by the main cells of the gastric mucosa. Pepsinogen is cleaved at acidic pH below 3 into the proteolytically active pepsin.

Pepsin is one of the important proteolytic enzymes in the digestive system. It is a phosphoprotein, or an endopeptidase which preferentially cleaves peptide bonds behind aromatic amino acids. The enzyme consists of 327 amino acids and has a molecular weight of about 35,000 daltons and a catalytic pH optimum of about 1.8. In non-acidic Mileu pepsin shows virtually no activity.