Development of a Radioimmunoassay for Bovine Pepsinogen A

Gastric aspartic proteases (AP) are among proteolytic enzymes that are widely distributed in vertebrates. They are responsible for the digestion of dietary proteins and are synthesized as inactive precursors (prochymosin, pepsinogen and progastricsin), commonly known as zymogens. One part of their secretion by mucous neck and chief cells in the gastric mucosa (2, 22, 23) reaches the blood stream allowing their measurement in the peripheral circulation. The determination of plasmatic concentrations of gastric aspartic proteases is conventionally performed by proteolytic assays, the first report having been described by Anson and Mirsky (4). The widest accepted measurement techniques are based on the estimation of the peptides released during incubation of the sample (at acidic pH) with a protein substrate (albumin or hemoglobin) added in high amounts (much higher than the endogenous content). The results are obtained by reading the optical density after addition of Folin-Ciocalteu’s color reagent. For routine diagnosis purposes, the proteolytic method was recently simplified by the use of multiwall plates and multireaders for the determination of the optical density (11, 21).