556 KINETICS OF BIOLUMINESCENT REACTION. II 



It has long been believed by many students of organic catalysis 

 that enzymes and their associated substrates must really be hetero- 

 geneous systems, and many facts have pointed indirectly to the 

 truth of this belief. In the present instance there can be no doubt 

 that lucif erase, the enzyme concerned, is a colloid, as are most enzymes 

 (Harvey, 1920)^ and a complex protein at that. There is every 

 reason, therefore, for expecting heterogeneity. 



Yet this expectation for enzyme reactions is rarely borne out by 

 the result of kinetical studies. In such heterogeneous systems the 

 rate of diffusion to the surfaces involved becomes an element in the 

 situation, but this factor is usually completely masked by the relative 

 rapidity of this diffusion as compared with the velocity of the reaction 

 itself. Thus Arrhenuis^" states : "The study of the velocity of reactions 

 in heterogeneous systems indicates that they behave very nearly in 



the same manner as homogeneous systems It depends 



on the circumstance that the difi'usion goes on so rapidly that it does 

 not perturb the chemical processes." 



Even in a reaction which proceeds as swiftly as that under consid- 

 eration, the diffusion rate must be even more rapid and therefore 

 negligible, for the temperature coefficient is high, as usual for enzy- 

 matic processes. During the major part of the reaction, therefore, 

 we must be measuring the rate of the oxidation process itself, and 

 no hint of the heterogeneous nature of the system can be derived 

 from the data. The initial flash is, however, in a different category, 

 and I believe that it must be argued that the momentary appearance 

 of this high reaction velocity when the enzyme is introduced is a 

 direct indication of the heterogeneity of the system, to be interpreted 

 in some similar way to that already stated for inorganic heterogeneous 

 catalysis. The details of the mechanism can not yet be stated. It 

 must be admitted that the surfaces of the enzyme particles can not 

 be conceived to be initially completely clean, since, from the manner 

 of their preparation, oxyluciferin is present. The major portion of 

 the surfaces involved may still be free from such reaction products. 



Under the experimental conditions of the present work it is certainly 

 not possible to reach the high concentration values which must 



^ Harvey, E. N., The nature of animal light, New York, 1920, 141. 

 ^"^ Arrhenius, S., Immunochemistry, New York, 1907, 142. 



