Crystal structure of human pepsinogen A

Human pepsinogen A is the inactive protein precursor of pepsin, an aspartic proteinase found in the stomach. Pepsinogen is synthesized in the chief cells and secreted into the gastric lumen. After pepsinogen has been exposed to the acidic pH of the stomach, a 47 amino acid, N-terminal prosegment is removed by autolytic cleavage to form the active enzyme.