Physicochemical Properties of the Proteolytic Enzyme from the Latex of the Milkweed, Asclepias Speciosa Torr. Some Comparisons with Other Proteases Iii. Kinetics of the Heat Inactivation of Papain, Bromelin, and Asclepain

The study of heat inactivation is often of considerable value in the characterization of proteolytic enzymes. This is true because in most cases these proteases appear to be inactivated at different rates at the same temperature and pH values. Also the determination of the inactivation velocity constants at different temperatures makes it possible to evaluate the critical thermal increment of the enzyme. The thermal inactivation of crystalline trypsin, chymotrypsin, and pepsinogen is completely reversible (1), so that the denatured inactive enzymes formed by heating the solutions revert to the native condition on cooling. In the present study of the thermal characteristics of three plant proteases, papain, bromelin, and asclepaln, 1 the heat inactivation could not be reversed by cooling the solutions. The rates of destruction of these enzymes do not show the great dependence on pH which pepsin exhibits (2). Near neutral pH, at constant temperatures, these plant proteases are inactivated at rates which can be described in most cases by simple equations. Differences in the state of purity do not seem sufficient to account for the individual behaviors of the enzymes.