124 THE NATURE OF ANIMAL LIGHT 



after four 1 c.c. additions, no more light is produced. The 

 luciferase is therefore used up and cannot oxidize more 

 than a certain quantity of luciferin. In this experiment, 

 however, we added a concentration of luciferin from one 

 Cypridina 100 times that of the luciferase from one Cypri- 

 dina, i.e., four additions each 25 times as concentrated. 

 We have, of course, no way of telling what the absolute 

 amount (in milligrams) of luciferin or luciferase is in a 

 single Cypridina^ but we do know that the luciferase from 

 one Cypridina cannot oxidize luciferin from more than 100 

 Cypridinas. If the ratio of luciferin to luciferase in a 

 single animal is 100 : 1, it would mean that luciferase 

 could oxidize 10,000 times its weight of luciferin. A large 

 excess of luciferin but not an indefinite quantity can be 

 oxidized by luciferase, and I believe this is sufficient justifi- 

 cation for considering luciferase an enzyme, although it is 

 not an ideal example of an organic catalyzer. Quite a num- 

 ber of enzymes are known to be diminished during the 

 course of the reaction they accelerate or to be poisoned by 

 their reaction products. Enzyme reactions inhibited by 

 the formation of reaction products again proceed if these 

 are removed or diluted. However, light does not again 

 appear in a mixture of weak luciferase with excess of lucif- 

 erin upon dilution with water, so that the luciferase cannot 

 have been merely inhibited by some reaction product but 

 must have been actually used up during the reaction. It 

 should be noted in passing that the peroxidases, ordinarily 

 spoken of as oxidizing enzymes, are used up in the reac- 

 tion and can only oxidize limited amounts of oxidizable 

 substances, a quantity almost in proportion to the con- 

 centration of peroxidase present. 



Whether luciferase is an oxidizing enzjrme made up of 



