Pepsin is one of the main proteolytic enzymes secreted by the gastric mucosa.
Pepsin consists of a single polypeptide chain and arises from its precursor,
pepsinogen, by removal of a 41 amino acid segment from the N-terminus.
Pepsinogen is synthesized in the stomach lining, and hydrochloric acid, also
produced by the gastric mucosa, is necessary to convert the inactive enzyme
and to maintain the optimum acidity (pH 1-3) for Pepsin function. Pepsin is
particularly effective in cleaving peptide bonds involving aromatic amino acids.
Pepsin shows extremely broad specificity; although bonds involving phenylalanine
and leucine are preferred, many others are also cleaved to some
extent. Pepsin A is a member of the subfamily A1 within the Pepsin family
and is the predominant endopeptidase in the gastric juice of vertebrates.
Pepsin A is inhibited by ovUS-1, a uterine Serpin.