240 



LIGHT AND LIFE 



bands with the same relative absorbances would also indicate that 

 the only difference between the reduced and oxidized forms is the 

 loss of two protons. 



The fluorescence emission spectra of luciferin and oxyluciferin 

 are shown in Fig. 19. The fluorescence emission j^eak of luciferin 

 is at 535, and for oxyluciferin, at 544 millimicrons. There appears 

 to be a very slight shoidder of blue fluorescence for oxyluciferin at 

 around 450-460 millinn'crons at acid pH. This is shown schematically 



150 



>- 



cn 



UJ 



UJ 



> 



UJ 



100 



50 



OXYLUCIFERIN 

 FLUORESCENCE 



luciferin 

 fluorescence" 





 430 450 



500 



550 



m 11. 



600 



650 



680 



Fig. 19. Ihioresecme spectra of luciferin and oxyUuiferin. The peaks are at ;)3r) 

 and 'AA milliniicrons, respectively. These data have been corrected for phototube 

 spectral efficiency. 



in Fig. 20, in which the peak energy levels for both absorption and 

 fluorescence arc shoAvn in analogy with an energy-level diagram for 

 atomic spectra. At the right of the diagram the absorption and fluores- 

 cence l>ands arc shown to indicate the degree of overlap among them. 

 The 460 millimicron fluorescence remains relativelv constant with 

 l)H. The reason why it is not seen at alkaline pW values is that the 

 544 millimicron band becomes very intense and overshadows the low- 

 intensity blue emissic^n with the spectrophotofluorometer used for 

 the measurements. It is of interest that although the absorption peak 

 shifts radically with changes in pH from acid to Ijase, the fluorescence 

 emission remains at 514 millimicrons although altering in intensity. 

 This would indicate that a separate portion of the molecule is re- 



