PepsinogenPDB ID: 3PSG
Pepsin is a digestive enzyme than cleaves proteins in our food. This structure shows pepsinogen, the inactive form of the enzyme. After it is secreted into the digestive system, a small portion is removed to form the active enzyme.
The high-resolution crystal structure of porcine pepsinogen.
Hartsuck, J.A., Koelsch, G., Remington, S.J.
Journal: (1992) Proteins 13: 1-25