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FIREFLY LUCIFERIN 



Physical and Chemical Properties 



The absorption spectrum of luciferin in solutions of various pH's in 

 the ultraviolet visible region of the spectrum appears in Fig. 1. The 

 shift in absorption was studied as a function of pH as was the fluores- 

 cence intensity. The change in fluorescence with pH is illustrated in 

 Fig. 2. From both these measurements it appears that luciferin has a 



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Fig. 1. Ultraviolet absorption spectrum of firefly luciferin at pH 1 and pH 13 in 

 water solution (0.1 M HCl and 0.1 M NaOH). 



pKa in the neighborhood of 8.5-8.6 (perhaps due to an imine group- 

 ing). The infrared absorption spectrum (Fig. 3) of a dry sample of 

 the purified luciferin was determined with a double-beam infrared 

 spectrophotometer (Perkin-Elmer) through the courtesy of Dr. Cam- 

 eron of the K-25 laboratories in Oak Ridge. Many materials which 

 were considered possible relatives of luciferin on the basis of some 

 of its other physical properties were also examined. Among them were 

 various pteridines, pyrimidines, purines, nucleosides, and nucleotides, 

 as well as riboflavin. Only the riboflavin and luciferin spectra exhib- 

 ited any marked resemblance from the 2- to 15-micron region. Of 

 particular note is the striking similarity in the absorptions of the 

 two compounds in the 10- to 15-micron region, some bands being 



