146 CHEMISTRY OF CYPRIDINA LUCIFERIN 



change in the structure of the molecule may have occurred during 

 its slow oxidation at pH 1.0. If the solution now be made acid again, 

 some of the original acid form of the spectrum is restored ( dotted line 

 curve of Fig. 4B). 



It is quite clear that solutions of luciferin purified in several 

 different ways possess very specific absorption in the visible and 

 ultraviolet regions of the spectrum. Furthermore, the spectrum 

 undergoes pronounced changes under various experimental condi- 

 tions. Were this absorption spectrum less complicated, one might feel 

 optimistic about the identification of Cypridiim luciferin from its 

 spectrum alone. Actually, the interpretation of an absorption spectrum 

 in terms of chemical structure can be very difficult and frequently 

 impossible unless other physical and chemical data are available. To 

 date we have not been able to find in the literature any known 

 compound whose absorption spectrum possesses the properties de- 

 scribed here, and at the present time it is not possible on the basis 

 of these measurements to make definite statements regarding the type 

 of organic molecule to which Ctjpridina luciferin belongs. The spectrum 

 may well prove of value in the ultimate identification, in conjunction 

 with other information which may become available. Certainly, the 

 ultraviolet absorption spectrum is proving an excellent criterion of 

 purity and, in this way at least, is aiding greatly in the isolation of 

 this extremely unstable compound. 



Fluorescence 



It has usually been stated that Cypriditia luciferin is nonfluorescent. 

 Certainly there is no marked fluorescence in solution characteristic of 

 such substances as quinine sulfate, oxidized flavins, acid luminol 

 solution, and various dyes. In this respect Cypriditia luciferin differs 

 from that of fireflies, which is highly fluorescent, bluish violet in weak 

 acid and yellow-green in alkali (Strehler and McElroy, 1949). 



However, it had been observed (Harvey and Chase, unpublished, 

 1941) that the brownish, solid, doubly cycled luciferin fluoresced 

 weakly yellow in the light from a mercury arc filtered through a Wood 

 nickel oxide filter. This light consists principally of radiation in the 

 near ultraviolet, the 365-m/x line. There was, however, no certainty 

 that the fluorescence came from luciferin. 



