PGA, pepsinogen I, PG I Protein (Active)

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. There are 2 related pepsinogen systems in man: PGA, formerly PG I, precursor of pepsin A, and PGC, formerly PG II, precursor of pepsin C. 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.

1. Frants, R. R., Pronk, J. C., Pals, G., Defize, J., Westerveld, B. D., Meuwissen, S. G. M., Kreuning, J., Eriksson, A. W. Genetics of urinary pepsinogen: a new hypothesis. Hum. Genet. 65: 385-390, 1984. 2. Sogawa, K., Fujii-Kuriyama, Y., Mizukami, Y., Ichihara, Y., Takahashi, K. Primary structure of human pepsinogen gene. J. Biol. Chem. 258: 5306-5311, 1983.