Crystalline Pepsin v. Isolation of Crystalline Pepsin from Bovine Gastric Juice By

A crystalline protein having powerful proteolytic activity has been described in previous papers of this series (1). This protein was isolated from commercial pepsin preparations which, in turn, had been prepared from the gastric mucosa of swine, t The possibility exists that this protein was formed from some more complicated compound during the process of extraction and does not represent the enzyme as secreted normally in the gastric juice. In order to determine whether the activity of the gastric juice is due to the same protein, experiments were undertaken to isolate the enzyme from gastric juice. Preliminary determinations of the activity of swine gastric juice showed that if the activity were due to the crystalline enzyme isolated from the gastric mucosa, the quantity of this protein in the gastric juice was extremely small and that a very large quantity of gastric juice would be necessarybefore any attempt at isolation could be made. I t was found to be impossible to obtain sufficient quantities of swine gastric juice but bovine gastric juice may be collected in quantity as described by Williams ~ (2). The contents of the fourth pouch of cattle was removed as soon as possible after the cattle had been killed in the slaughter house. About 1⁄2 liter of juice was obtained from each animal and larger quantities were found in those animals which had been recently fed. The juice obtained in this way contained more or less undigested food and fil-