Pepsinogen 4, Group I (PGA4)

PGA4 belongs to the peptidase A1 family. The predicted amino acid sequence of human pepsinogen consists of 373 residues and is 82% homologous with that of swine pepsinogen. The predicted sequence contains 15 amino acid residues at the NH2 end, showing that the protein is synthesized as a prepepsinogen. In human gastric mucosa, 2 immunologically distinct classes of pepsinogen are synthesized. PG1 is restricted to the corpus, while PG2 is found throughout the stomach as well as in the proximal duodenum. PG1 is found in serum and urine in a ratio of about 1 to 10. PG2 is present in serum and seminal fluid but only trace amounts are found in urine. Serum PG1 and PG2 apparently originate from the stomach in the main, because the levels are very low after gastrectomy. PG2 in seminal fluid probably originates from the prostate.