BERNARD L. STREHLER 



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nearly identical, others being slightly displaced from each other (see 

 Fig. 3). These similarities would seem to indicate that luciferin and 

 riboflavin have a predominantly similar general architectural design 

 and that they differ considerably in the nature of the substituents on 

 this framework. 



Fig. 2. Fluorescence intensity as a function of pH. The fluorescence was excited 

 with the 365-millimicron Hg hne. The pH was varied gradually and pH 

 and fluorescence measured simultaneously. 



The electrophoretic mobility of luciferin as a function of pH was 

 determined, and the results are indicated in Fig. 4. Here a pKa in 

 the region of pH 3-4 and pH 8-9 are apparent. The more acidic 

 dissociation is probably due to a carboxyl group. In Fig. 5 is illustrated 

 the polarographic half-wave of luciferin. The £o suggested by this 

 half-wave is quite far on the reducing side of the hydrogen zero, al- 



