E. NEWTON HARVEY 7 



been definitely established only among the elaterid and lampyrid 

 beetles. 



The absence of an ATP reaction does not necessarily mean that ATP 

 plays no part in light production (McElroy and Harvey, 1951). It 

 ma\' indicate that other components of the luminescent system are 

 lacking and that further analysis may be necessaiy to designate the 

 complete system. Similarly, the absence of a luciferin-luciferase reac- 

 tion may indicate that accessory substances are lacking or that lucif- 

 erin and luciferase are particularly unstable substances in the group 

 of luminous organisms tested. 



In view of the recent work (Strehler, 1953; Strehler and Cormier, 

 1953; McElroy, Hastings, Sonnenfeld, and Coulombre, 1953; Strehler, 

 Harvey, Chang, and Cormier, 1954) on bacterial luminescence, where 

 the luminous system is complicated by accessory substances such as 

 long chain aldehydes, as well as in firefly luminescence requiring high 

 energy phosphates, a redefinition of lucif erin becomes necessary ( Har- 

 vey and Tsuji, 1954). It is no longer sufficient to claim that luciferin 

 is present in a boiled extract of luminous tissue, whereas the dark 

 cold water extract contains luciferase. McElroy has demonstrated that 

 dark cold water extracts of firefly (Photinus pyralis) lanterns emit 

 no light when purified pyralis luciferin is added, but do luminesce with 

 ATP. Therefore the cold water extract (luciferase) lacks ATP in- 

 stead of luciferin. ATP is the limiting factor under these conditions. 

 Rather than placing the emphasis on the limiting factor, or on heat 

 stability or dialyzability, as has been done previously, light emission 

 should be the criterion for luciferin. In the case of luminous organisms 

 requiring dissolved molecular oxygen for luminescence, luciferin may 

 properly be defined as the oxidizable substance supplying molecules 

 capable of absorbing enough excess energy from a chemical reaction 

 to emit in the visible region. Such a definition implies that some form 

 of luciferin molecule — either free base or acid, either dissociated anion 

 or cation, in reduced or oxidized form, either free or combined with 

 protein, like a prosthetic enzyme group — can pick up the energy of 

 the oxidative reaction in which it is involved. Such a definition does 

 not mean that luciferin is the same substance in different luminous 

 animals, nor does it necessarily designate luciferin molecules them- 

 selves as the ones which emit, but it does imply that a related mole- 



