Studies on gastric proteolysis. 3. The secretion of different pepsins by fundic and pyloric glands of the stomach.

It has been shown (Desreux & Herriott, 1939; Northrop, Kunitz & Herriott, 1948; Hoch, 1950; Merten, Schramm, Grassmann & Hannig, 1952; Taylor, 1956, 1959b) that crystalline swine pepsin contains more than one proteolytically active component. Merten et al. (1952) and Taylor (1959b) have also found more than one proteolytic component in pooled human gastric juice. The latter described two electrophoretically homogeneous components of human gastric juice which moved to the anode at pH 2-5 in the Tiselius apparatus and thus resembled pepsin. Each component digested serum albumin with two pH maxima, one near pH 2 and the other near pH 3.5. The origin of these active components of crystalline pepsin and gastric juice has not been satisfactorily settled. As Northrop et al. (1948) point out, crystalline pepsin from a single individual animal has never yet been isolated, so that different components may represent nothing more than pepsins from the different individuals who contributed to the original starting material. However, in the electrophoretic experiments mentioned above the gastric juice from which the two anodal-moving components were prepared was contributed by only two normal subjects; the pH maxima for digestion by the smaller component were at lower pH values than those of the larger, whereas the pH-activity curves of theoriginal juice of each subject showed maxima close to those of the larger component. It seemed therefore that the smaller component was not the main pepsin of either of the individuals but a substance with its activity masked in the original juices. This evidence suggests that there might be in each individual at least two pepsins, each exerting proteolytic action with two maxima below pH 5, but with definite differences in the pH values at which the maxima occur. A further clue to the origin of these components arose during the investigation of the proteolytic activity of extracts of gastric mucosa from different parts of the stomach (removed at operation) of patients with gastric or duodenal ulcer. Extracts of pyloric mucous membrane often gave