Pepsinogen A is secreted exclusively by the chief cells of the gastric corpus. The levels of Pepsinogen I correlate directly with the active number of chief cells in this area. In cases of severe atrophic gastritis of the corpus region, the chief cells will be destroyed and the levels of Pepsinogen I will fall dramatically.Pepsin is one of the main proteolytic enzymes secreted by the gastric mucosa. It consists of a single polypeptide chain and arises from its precursor, pepsinogen, by removal of a 41-amino acid segment from the amino end. Pepsin is particularly effective in cleaving peptide bonds involving aromatic amino acids. Samloff and Townes (1970) showed that the pepsinogen-5 derived from the stomach and excreted in the urine is absent in some persons. Family and population data supported the view that absence of PG-5 is recessive.