E. NEWTON HARVEY 135 



tion of luciferin, is, therefore, not to be compared to the reactions 

 in cells giving rise to the carbon dioxide of respiration. As I have 

 previously suggested^ it is probably of a type similar to the oxidation 

 of a leuco dye to the dye itself. In the case of methylene blue this 

 reaction may be represented as follows: 



Leucomethylene blue (CieHjoNaSCl) + O ±1^ methylene blue (CieHisNsSCl) + H2O 



In the case of luciferin we may have 



Luciferin (LH2) + O ±1; oxyluciferin (L) + H2O 



Whether the oxidation of luciferin really proceeds with the for- 

 mation of H2O or whether it involves the actual addition of oxygen, 

 as in the oxidation of hemoglobin, is uncertain. Like methylene 

 blue and oxyhemoglobin the oxyluciferin can be again reduced^ but 

 the reduction resembles that of methylene blue in that it will not 

 take place by the mere removal of oxygen, as will the reduction of 

 oxyhemoglobin, but requires also the addition of some reducing 

 agent. 



The fact that the reaction luciferin-oxyluciferin is reversible is in 

 itself evidence that no carbon dioxide is produced. Reactions re- 

 sulting in CO2 production involve considerable energy changes (heat 

 production) and are reversed only with the greatest difficulty and 

 with the addition of a large amount of energy. Whether any con- 

 siderable amount of heat is produced during oxidation of luciferin 

 will be discussed in the following paper. 



8 Harvey, E. N., J. Gen. Physiol, 1918-19, i, 133. 



