Pepsin A (Pepsin)

Pepsin A is a major digestive enzyme in humans and many animals, classified as an aspartic protease, responsible for breaking down proteins into smaller peptides in the acidic environment of the stomach[3][4][5]. It is initially synthesized as the inactive precursor pepsinogen, secreted by chief cells in the gastric mucosa, and activated by stomach acidity (pH 1.5–2.5)[1][3][4]. Pepsin A exhibits broad substrate specificity, with optimal cleavage adjacent to hydrophobic and aromatic amino acids (such as phenylalanine, tryptophan, and tyrosine)[3][4]. This enzyme facilitates the initial stage of protein digestion prior to further processing by other intestinal proteases, contributing significantly to nutrient absorption[2][3][4][5]. Aberrant pepsin activity—particularly if present in the esophagus, airways, or other tissues due to reflux—can cause mucosal damage and contributes to diseases such as GERD, LPR, and peptic ulcers[4][5]. Pepsin can be inhibited by compounds such as pepstatin, and measurement of pepsin or pepsinogen in body fluids serves as a biomarker for certain gastric pathologies[4][5].

Other names

PepsinPepsinogen A (its zymogen/precursor)PEP

Acid protease inhibition (competitive inhibition of the aspartyl active site), protease substrate cleavage