196 BIOCHEMISTRY OF FIREFLY LUMINESCENCE 



light reaction. One difficulty remains, however, and that is that even 

 with an excess of inorganic pyrophosphatase the light is never en- 

 tirely extinguished in the in vitro reactions. It is not unlikely, how- 

 ever, that in the intact firefly the low concentration of active inter- 

 mediate can be rapidly oxidized by components other than molecular 

 oxygen. A brief period of anaerobic conditions may allow the accu- 

 mulation of an active intermediate to sufficient concentration that it 

 can react significantly with molecular oxygen to give light. Further 

 work on the physiology and biochemistry of the flash reaction will 

 be necessary before a decision can be reached with respect to these 

 various hypotheses. 



Mechanism of Luminescence — Function of ATP 



The response of crude extracts of numerous species of fireflies to 

 ATP has now been tested (McElroy and Harvey, 1951). All have 

 given a positive response. In some cases it is necessary to supplement 

 even the crude extracts with additional luciferin before significant 

 amounts of light can be obtained with ATP. It would appear from 

 these experiments that the luciferins of the various firefly species are 

 identical. Additional experimental work is necessary to establish this 

 point definitely. Numerous other luminous forms have been tested 

 for their ability to respond to ATP and thus far positive results have 

 been obtained only with the lympyrid and elaterid beetles (Haneda 

 and Harvey, 1954). The significance of this fact is not clear, but it 

 may be related directly to the mechanism of control of the light emit- 

 ting reaction. In Cijpridina, for example, the luminescent components 

 are liberated from separate glands into the surrounding sea water 

 where they mix, react, and emit light. In other words, the luciferin 

 must be chemically prepared to react immediately without previous 

 dark reactions. This instability in the luciferin molecule is apparent 

 when it is isolated from the dried Cypridina. In the presence of oxy- 

 gen but in the absence of luciferase it rapidly oxidizes without light 

 emission. This is in conti-ast to firefly luciferin which is relatively 

 stable when purified. Apparently certain dark reactions are essential 

 before it can be oxidized, even in the presence of luciferase. Adeno- 

 sine triphosphate is essential for this activation process. It now seems 

 likely that firefly luciferin and ATP in the presence of luciferase and 



