172 



BIOCHEMISTRY OF FIREFLY LUMINESCENCE 



The piifified enzyme results in Fig. 6 demonstrate that the initial 

 light intensity varies, both with the Mg++ and ATP concentration in 

 a manner suggesting a complex between the two molecules. This is 

 particularly noticeable with low Mg++ concentrations where it is 

 possible to demonstrate an inhibition with high concentrations of ATP. 

 For the intermediate range of concentrations the maximum initial 

 light response is obtained with a ratio of ATP to Mg++ of approxi- 



70 



OOlMg CONC. 



4 6 8 10 12 14 



ATP CONC. MOLAR X 10* 



Fig. 6. The effect of varying ATP and Mg concentration on initial light intensity 

 .(McEbroy et al, 1953). 



mately 1. In addition to the effect of Mg++ on the initial light 

 intensity, there is also a noticeable influence on the decay and final 

 baseline level. The results of such an experiment are presented in 

 Table IV. 



In purified enzyme preparations, light emission cannot be elicited 

 by a variety of other phosphorylated compounds which have been 

 tested. The initiation of light emission in the crude extracts by ADP 

 is due to the presence of an effective myokinase. Inosine triphosphate, 

 uridine triphosphate, acetyl phosphate, creatine phosphate, inorganic 

 pyrophosphate, and a variety of other phosphorylated and nonphos- 

 phorylated cofactors fail to initiate light. The specificity of response 



\ 



of the firefly extracts has proved useful as a tool for ATP assay in 

 various systems (Strehler and Totter, 1952; McElroy, unpublished). 



