ISOLATION AND PROPERTIES OF CRYSTALLINE pAPAIN*

Proteolytic enzymes from plant tissues have in general resisted purification more successfully than those of animal origin. Proteinases have been extracted from many plants, among them yeast (9), pineapple (27), pumpkin (27), beans,’ and wheat (4), but much concentration and purification are usually required before a preparation of even moderate activity is obtained. This presents difficulties similar to those encountered in obtaining tissue enzymes from animal material. On the other hand, the investigation of latex is a comparatively simple matter, for ‘an initial high degree of purity is often found. For unpurified papaya latex the proteolytic activity on hemoglobin per unit of protein nitrogen is already one-fourth to one-half that of the crystalline pancreatic enzymes. In the papaya the latex appears to be a specialized enzyme-bearing material comparable in this sense to pancreatic or gastric juice. There is no apparent distinction between latex-borne and other plant proteinases as such, possibly because the source of the latter may also have been a system of latex vessels. The proteinases of beans, wheat, and pineapple, as well as ficin and papain, may be activated by HZ’S, HCN, and similar reducing agents, and inactivated by iodoacetic acid, hydrogen peroxide, and other oxidants. These enzymes are therefore all to be classed as papainases, as suggested by Waldschmidt-Leitz (24).2 On the