174 



BIOCHEMISTRY OF FIREFLY LUMINESCENCE 



erin concentrations the light intensity decreases faster than at low 

 concentrations of luciferin. This variation in the rate of light intensity 

 decay results in an inverse relationship of light intensity to the lu- 

 ciferin concentration after the reaction has proceeded for 2 to 3 

 minutes. 



The rate of the light intensity decay can be obtained by taking the 

 slope of the straight line which results from plotting the log light 



2 4 6 8 10 



ENZYME CONC. Mix 10^ 



Fig. 8. The effect of luciferase on the initial Ught intensity and the rate of com- 

 plexing (McElroy et al, 1953). 



intensity versus time for the first 10 seconds of the reaction. By plot- 

 ting the rates obtained against the corresponding luciferin concentra- 

 tion the relationship shown in Fig. 7 is obtained. The results demon- 

 strate clearly that the rate at which the light intensity decreases 

 depends upon the concentration of luciferin in much the same way as 

 the initial light intensity depends upon this factor. Similar results 

 were reported above for varying concentrations of Mg++ ions, i.e., 

 the steady-state level of luminescence was higher with a low Mg+ + 

 ion concentration. 



