CRYSTALLINE PAPAIN

Abstract

The proteolytic enzymes of papaya latex have been known for many years and have been extensively investigated (1, 2). However, until Balls and coworkers reported the crystallization of papain (3, 4) and chymopapain (5) from fresh papaya latex, only crude or partially purified preparations were studied. The preparative procedures of these investigators have not been extensively applied because of the scarcity and high cost of fresh papaya latex. As a result, few studies have been made of crystalline papain, especially since it has not been generally possible to obtain the crystalline enzyme from commercial dried latex. We have been able to prepare crystalline papain in good yield from a source of commercial dried papaya latex, but it should be emphasized that not all commercial products have given satisfactory results in our hands. This first paper describes in some detail the method of obtaining crystalline papain. Although much of the procedure is that of Balls and Lineweaver (4), it is obviously desirable, for an enzyme which has stimulated so much interest, to have the complete preparative scheme in one place. The preparation of a crystalline mercury derivative of papain (mercuripapain) and an analysis of some factors influencing the activity of the enzyme are also given. It was previously shown (2) that partially purified preparations of papain hydrolyze many types of synthetic peptide derivatives; similar results have now been obtained with the crystalline enzyme. Papain also has a powerful esterase activity and in this respect resembles the animal proteinases, trypsin and chymotrypsin, but differs from them in possessing an essential sulfhydryl group and in not being inhibited by diisopropyl fluorophosphate. Later reports in this series will be concerned with additional physical