J. WOODLAND HASTINdS AND VERNON C. BODE 303 



I/) 



3 



M 



U 



50 

 40 



30- 

 20- 



4- 



TIME 



MINUTES 



Fig. 7. This figure shows tlie rates of inacti\ation of Gonyaulax luciferase at 

 several diffcient tcinpcratiiies. Vhe enzyme used was the active fraction from a 

 first ammonium sulfate precipitation (see Table 1). In all ciuves except one, 

 enzyme alone was present during the incubation. In one (dotted line), the enzyme 

 was incubated in the presence of 2 M NaCl. Aliquots were removed from the 

 incubation mixtures at the times indicated and assayed for enzyme by measuring 

 the initial intensity of luminescence in a reaction mixture with added luciferin. 



An effect of added salt upon the enzyme is evident from the fact 

 that enzyme is more unstable in the presence of salt. This is illus- 

 trated in Fig. 7, where the curves show the rate of denaturation at 

 different temperatures. All curves are for enzyme alone except the 

 dotted line, which is enzyme in the presence of salt, at 31 °C. The 

 velocity constant for heat denaturation of the enzyme is much greater 

 with added salt. In addition, the rate of denaturation is greater at 

 higher salt concentrations. 



An Arrhenius plot of these data (Fig. 8) reveals that the slope 



(which defines the enthalpy of activation) is the same in the presence 



and in the absence of the salt. But the temperature range in which 



denaturation occurs is different, and indicates an increase in the 



entropy of activation with added salt. 



