Isolation of Crystalline Pepsinogen from Swine Gastric Mucosae and Its Autocatalytic Conversion into Pepsin

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Abstract
Crystalline pepsinogen (propepsin) was isolated from swine gastric mucosa; it is a colorless protein crystallizing in finely acicular crystals from 0.4 saturated (NH4)2SO4 solutions at a pH of 5.2 to 5.6, and is purified by recrystallization. Optical rotation and proteo-lytic activity were constant for crystals from different sources. It differs from pepsin in not clotting milk at pH 5 and not liquefying gelatin at pH 4.7. Pepsin was prepared from pepsinogen by acidification, and was indistinguishable from crystalline pepsin prepared by Northrop''s method. The optical activity and proteolytic activity of pepsin from pepsinogen, and commercial pepsin, were nearly the same. Conversion of pepsinogen to pepsin at pH 4.6 was autocatalytic, as was the case with trypsinogen to trypsin also. Little non-protein-N was liberated during the conversion, which is probably a rupture of a peptide linkage. The method of preparing pepsinogen is given in detail.

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