Bioluvtinescence 669 



tion of the two photogenic substances (0.008 sec.)-^ This suggests that the 

 reaction between luciferin and luciferase is slow, compared with the rate 

 of the reaction which involves the oxygen. 



Cypridina luciferin is apparently oxidized in two ways: (1) through action 

 of luciferase, with light emission, and (2) through other than luciferase ac- 

 tivity, without light production."* The latter reaction, but not the former, 

 seems to be reversible in the presence of reducing agents such as Na2S204 or 

 H2S, or in the presence of finely divided platinum and free hydrogen, or at 

 the cathode of an electrolyzed extract, or simply under the reducing action of 

 some cultures of bacteria. This freshly reduced luciferin is able to emit light 

 when oxidized in the presence of luciferase. Luciferin oxidized in the pres- 

 ence of luciferase is not capable of being reduced again by such reducing 

 agents, hence the oxidation in the presence of luciferase must be substan- 

 tially different from oxidation by other oxidizing agents. 



For many years it was the accepted hypothesis that luciferase not only 

 catalyzed the oxidation of luciferin but also was the molecule which actually 

 emitted the light. The lights of the two genera of fireflies, Photiiris and 

 Phothnis, whose luciferin and luciferase are capable of reciprocal interaction 

 with light production, are of visibly different colors.^- In Photinus it is more 

 reddish; in Photurns, more yellowish. When the luciferases and luciferins 

 are interchanged in in A'itro experiments, the color of light emitted is char- 

 acteristic of that species which contributes the luciferase. In view of these 

 and other characteristics of the reaction, the following scheme for the light 

 emitting reaction was proposed: 



(Luciferase) 



Luciferin + Vi Oj ^ - =^ Oxidized luciferin* -f H2O 



Oxidized luciferin* -f Luciferase > Oxidized luciferin + Luciferase* 



Luciferase* > Luciferase + hv 



*indicates an activated molecule 



These observations, which at one time seemed definitely to indicate luci- 

 ferase as the actual light-emitter, now appear capable of other interpretations. 

 This situation could possibly obtain, for example, if the light emitter were 

 a conjugated protein with luciferin as an emitting prosthetic group, or if 

 luciferase were the specific protein and luciferin the coenzyme of a reacting 

 system. 



Detailed studies of the spectrographic changes in luciferin during its oxi- 

 dation both in the absence and in the presence of luciferase have since in- 

 dicated that the steps are the same in the two instances.'" Reduced Cyj)ridina 

 luciferin with a maximum absorption at 435 m/x becomes oxidized to a form 

 with a maximum absorption at 465 m/x, and then this latter form is de- 

 stroyed. The total amount of light produced is proportional to the initial 

 amount of absorption at 435 m/t. The rate of these oxidative changes is 

 about 100 times as rapid in the presence of luciferase as in its absence (Fig. 

 253). 



Such ()bser\'ations as the foregoing, and further detailed studies of the kin- 

 ctics of the bioluminescent reaction,'*" together with an observation that luci- 

 ferin in 95 per cent ethyl alcohol at .70° C. will luminesce,-'' have given 



