Preparation and Properties of Crystalline Salmon Pepsin*

The techniques of crystallization, developed in recent years, have permitted enzyme studies that are far more exact than were possible with the more crude preparations. Among the crystalline enzymes, Northrop’s pepsin has been the object of widespread and intensive research (1) which has contributed to the knowledge of enzyme action and mode of operation. In order to further the understanding of pepsin, it seemed worth while to begin comparative studies on pepsins from sources other than beef and swine. In the work to be described the pepsin of the Pacific Coast king salmon (Oncorhynchus tschawytscha) was crystallized, and comparative studies have been begun. Methods for crystallizing swine pepsin have been described by Northrop (2) and Philpot (3). Fortunately, the techniques for handling mammalian pepsin and pepsinogen (4) have been found applicable, with some modification, to fish pepsin. g!Most of th e s used as sources of material were caught in fi h traps at La Conner, Washington, and brought under ice to Seattle, where they were dressed, after having been about 18 hours out of water. The stomachs were removed, cleaned, and stored frozen; about 100 were required for each kilo of mucosa. The stomachs from actively feeding fish, caught at sea, were larger and contained more pepsin, but were difficult to ship successfully to Seattle.