448 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1960 



mononucleotide. Oxidized luciferin is reduced by diphosphopyridine 

 nucleotide, under the influence of a specific oxidase, and thus a constant 

 supply of luciferin is maintained. 



Many years ago it was suggested that luminescence in living organ- 

 isms was derived from cellular respiratory mechanisms. This is borne 

 out by the situation in luminous bacteria, in which light is emitted 

 during the course of the reversible oxidation of a flavin complex. 

 Riboflavin nucleotides participate as coenzymes in the oxidation-re- 

 duction reaction of cells. The light emitted during the oxidation of 

 dihydroflavin mononucleotide in luminous bacteria can therefore be 

 regarded as an accidental byproduct of the reaction. This situation 

 helps us to understand how luminescence has appeared so frequently 

 and independently throughout the animal kingdom, from unicellular 

 protozoa to fishes. Presumably, slight changes in preexisting respira- 

 tory pathvrays have been exploited to achieve light production. There 

 is a wood fungus, Panus stipfwus, which exists in luminous and non- 

 luminous forms, and luminosity is inherited as a single pair of charac- 

 ters dominant over nonluminosity. Thus, a slight change in genetic 

 constitution may be enough to confer luminescence on an organism. 



Other detailed biochemical investigations have been concerned with 

 the luciferins of a small ostracod crustacean {Cypridina) and the fire- 

 fly. Neither of these substances has yet been identified chemically 

 with certainty, but enough is loiown about their composition to show 

 that they are dissimilar from each other and from bacterial luciferin. 

 It has just been demonstrated that the luciferin of the piddock 

 (PJiolas), a marine bivalve mollusk, is reduced flavin mononucleotide. 

 Luminescence in PlwJas thus conforms to the bacterial system. 



There is obviously much diversity in the chemical composition of 

 luciferins found in different creatures, and this is confirmed by other 

 lines of evidence. Emission spectra of the luminescence of different 

 creatures are often dissimilar, indicating tliat different substrates or 

 luciferins are involved. Cross tests made with the luciferin of one 

 animal and the luciferase of another have been positive, that is, have 

 resulted in light emission only when the animals are closely related; 

 e.g., different species of fireflies. Again, these results point to much 

 specificity in the luciferins and luciferases of different gronps. A 

 curious exception concerns a small crustacean Cypridina and a fish 

 Apogon^ both from Japan. The luciferin of the one gives a positive 

 cross-reaction with the luciferase of the other, and this is the only 

 positive result that has been obtained, of many tried, with luciferin 

 and luciferase of Cypridina against luminous extracts of other ani- 

 mals. It implies close similarity in the biochemical mechanisms of 

 these two unrelated species. 



