Protease means a vertebrate gastric juice proteases, endonucleases typically is a peptide chain, broad substrate specificity, but of the hydrophobic amino acid residues adjacent to the peptide bond can be considerable hydrolysis. Isoelectric point at pH = 1 nearby. PH activity optimum of about 2 (to denature the protein as substrate at about 3.5). In addition to obtain a main component pigs protease A (EC3.4.23.1) also outside the protease B and C. To form a variety of proteolytic enzymes are inactive precursor of protein zymogen (pepsinogen) A, B, C of the secreted, self-catalytic acidic conditions in the gastric fluid and to start. The isoelectric point of the protein enzyme A is the original pH3.7, molecular weight of about 40,000. Amino-terminal residues are leucine. Cut at startup under several peptides from the amino terminus, and the remaining portion, having a molecular weight of about 33,500, into the amino-terminus of the protein having isoleucine enzyme A. Then the peptide was excised protease inhibitory activity of some action. Protease B and C and A have very similar properties (substrate specificity is also slightly narrower than A), changes are also the same start. Decomposition of gelatin B is strong. Presumably, it has been called gelatinase (gelatinase) is the same substance. The activity of proteolytic enzymes is that two aspartic acid residues play an important role. PP when more normal gastric ulcer; significantly increased when duodenal ulcer; chronic duodenitis, gastric dilatation, chronic gastritis when activity weakened; little or no activity when pernicious anemia. PGⅠ, PGⅡ elevated levels prompted an increased risk of peptic ulcer, PGⅠ judging ulcer activity levels increased sense. PGⅠ / PGⅡ ratio at the time of gastric cancer and atrophic gastritis were significantly reduced, suggesting that this examination can be used as a tracing atrophic gastritis indicators and early detection of gastric cancer screening methods.