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BIOCHEMISTRY OF FIREFLY LUMINESCENCE 



are again extracted with ethyl acetate, and the latter is concentrated 

 by vacuum distillation. The luciferin is finally concentrated in water. 

 At neutral pH luciferin has two characteristic absorption maxima, one 

 major peak at 330 and a secondary peak at 263 ni/x. The exciting 

 wavelength for fluorescence corresponds to the adsorption peak at 

 330 m/x. The concentrated luciferin is slightly yellow in alkaline solu- 

 tion, but it changes to a colorless solution in weak acid. In the former 

 case the fluorescence upon ultraviolet activation is an intense yellow- 

 green, whereas in the latter case the fluorescence changes to a pale 



5.5 60 65 70 75 80 85 90 



P H 



Fig 2. Effect of pH and buffers on firefly luminescence (McElroy and Strehler, 

 1949). 



red. The luciferin can be maintained for several weeks without 

 appreciable loss of activity either frozen in the aqueous solution or in 

 the dried state. In aqueous solution at pH 3.5 and 100° C complete 

 inactivation occurs in 15 minutes, and there is approximately 50% loss 

 of activity in 5 minutes. At pH 10 less than 5% inactivation occurs in 20 

 minutes at 80° C. The inactive luciferin can be removed from the 

 active by extraction with ethyl acetate at pH 3.5. Under these condi- 

 tions only the latter is removed from the aqueous phase. The physico- 

 chemical properties of firefly luciferin are discussed in the following 

 paper (Strehler and McElroy). 



