1904] Studies on Enzyme Action. 213 



catalysis of hydrogen peroxide by hsemase may be briefly considered. 

 In this connection it must, in the first place, be taken into consideration 

 that we are dealing with a heterogeneous reaction, since the hsemase is, 

 in all probability, present in the solution in a colloidal state. According 

 to our present views, such solutions form a two-phase system, the 

 colloid being suspended in the liquid in a very fine state of division. 



It has recently been insisted upon, more particularly by Nernst,* 

 that we are not entitled to apply the equations governing reaction 

 velocity in homogeneous systems to heterogeneous systems. 



According to Nernst there is always equilibrium at the boundary 

 surface between two phases, and the changes which take time are (1) 

 chemical actions in the two phases, and (2) diffusion of substances to 

 and from the boundary. Examples of the first type, in which the 

 reaction velocity in one of the two phases is slow compared with the 

 rate of diffusion, are given in the paper quoted; reactions of the 

 second type, in which the velocity of diffusion determines the rate of 

 action, have been experimentally investigated by Brunner.f 



It may be taken as proved that the rate of solution of marble in 

 acids is conditioned by a diffusion process, and the same is true of 

 the rate of combination of hydrogen and oxygen in contact with a 

 platinum surface. One criterion for the dependence of a reaction 

 velocity upon diffusion is the effect produced by stirring the solution- 

 this shortens the diffusion path, and thus increases the speed of 

 reaction. 



Nernst \ is also of opinion that the same explanation holds for the 

 decomposition of hydrogen peroxide by colloidal platinum that the 

 actual decomposition is very rapid compared with the diffusion of the 

 peroxide to the surface of the catalysor. 



We will now inquire whether the catalysis of hydrogen peroxide by 

 hsemase can be represented in a similar way. Since the particles of 

 a colloidal solution are in a continual state of motion, we may assume 

 that stirring would not appreciably affect the reaction velocity. We 

 may imagine that each particle of colloid has adhering to it a layer of 

 liquid ; that the rate of decomposition of the peroxide by the enzyme 

 is very great, and that the concentration outside the adhering layer is 

 kept constant by the motion of the colloidal particles. The rate of 

 decomposition of the peroxide would then be determined by the rate 

 of its diffusion through the adhering film, and, since the rate of 

 diffusion is proportional to the difference of concentration on the two 

 sides of the film, a simple explanation would be given of the observed 

 fact that the reaction velocity is proportional to the concentration of 

 the peroxide. Some support is given to this view by the fact that the 



* Nernst, 'Zeit. pliysik. Chemie,' vol. 47, p. 52 (1904). 

 t -Bmnner, ' Zeit. physik. Chemie,' vol. 47, p.. 56 (1904). 



Loo. dt. :: 



