170 



BIOCHEMISTRY OF FIREFLY LUMINESCENCE 



Quantitative Response to ATP and Mg Concentration 



One of the interesting characteristics of the crude luminescent 

 system was the rapidity with which ATP was apparently utilized. In 

 crude extracts, the light emission was correlated with the disappear- 

 ance of ATP and the appearance of inorganic phosphate. When the 

 two equivalents of phosphate from ATP were liberated, the light 

 emission of the preparation ceased. A second addition of ATP 

 restored the luminescence (McElroy, 1947). On the other hand, when 

 ATP was added to any of the partially purified preparations, there 



5 6 7 8 9 10 

 TIME-MINUTES 



11 12 13 14 15 



Fig. 5. Light intensity-time relationships for firefly luminescence using partially 

 purified preparations. Secondary addition of ATP at 5 and 12 minutes 

 (McElroy and Strehler, 1949). 



was initially a very bright light response, which rapidly decreased to 

 a basal level of approximately 10 to 15^ of the maximum (Fig. 5). The 

 low residual luminescence has been observed to last over a period of 

 more than 15 hours. The light intensity of this preparation may be 

 increased by a second addition of ATP. The results definitely indicate 

 that ATP concentration was the hmiting factor, as far as hght in- 

 tensity was concerned. Contrary to observations in the crude prepara- 

 tions, however, was the fact that no inorganic phosphate appeared 

 as the ATP was apparently consumed. Several different experiments 



