Pepsinogen A5/PGA5: ProductsPepsins are aspartic proteases that are synthesized in the gastric mucosa and secreted into the stomach. They are released as zymogens called pepsinogens and then converted to active pepsins by the acidic pH of gastric juices. PGA-3, PGA-4, and PGA-5 are isozymogens of human Pepsinogen A, which differ in amino acid sequence by 2 - 4 residues. This recombinant human Pepsinogen A corresponds to PGA-4. Pepsins have optimal activity under conditions of acidic pH and are inhibited by pepstatin. Pepsin A has broad substrate specificity, but preferentially cleaves peptide bonds involving aromatic and aliphatic amino acids.