116 SPECTROSCOPIC INVESTIGATIONS 



methylketone, the hydroquinone of van der Kerk's hypothetical com- 

 pound 



OH 



-COCH2OH 



OH 



is very similar to the corrected inactivation spectrum, Fig. 10. 



These observations were made in 1947. We immediately tested the 

 compound with luminous bacteria and with Cijpridina luciferase 

 (Spruit, 1949a), but without success. In view of the number of hy- 

 potheses upon which our attempt was based, this was not very sur- 

 prising, and as there is no immediate way of further testing the idea, 

 this is where our story could come to an end. However, during the 

 years that followed, new contributions were made by other workers 

 to the subject of bioluminescence, and apart from van der Kerk's 

 inactivation spectrum we have now two more spectra of compounds 

 involved in bioluminescent reactions. One is the absorption spectrum 

 of purified Cijpridhui luciferin, measured by Chase and Brigham 

 (1951); the other is that of the stimulating factor in the luminescence 

 of the firefly Photimis pyralis, measured by Strehler and McElroy 

 ( 1949 ) . A comparison of these spectra serves to extinguish our last 

 hope that the various forms of bioluminescence might be related. It 

 is certain that these three spectra belong to widely different classes 

 of compounds. We also have to conclude that most of the arguments 

 in favor of van der Kerk's proposal are of doubtful value, and the 

 nature of the compound involved in the photochemical inactivation 

 is therefore still unknown. 



Notwithstanding these criticisms, the remarkable similarity between 

 the inactivation spectrum of the bacteria and the absorption spectra 

 of certain derivatives of naphthohydroquinone is striking. It is hard 

 to believe that this similarity is completely meaningless. We must 

 recall here also the magnificent work by van Schouwenburg (1938), 

 which has given a firm basis to the theory that in the bacterium Ph. 

 phosphoreum the luciferin is reversibly oxidizable and reducible, a 



