E. ACKERMAN, G. K. STROTHER AXD R. L. BERGER 27 



creasing tlit' length of an encounter. If the encounters are sufficiently long, 

 a reaction will occur for each encounter. Then the reaction rate will vary 

 with the diffusion rate. If, on the other hand, the prol)al)ility of reaction 

 is lower, so that most encounters do not lead to a reaction, then the re- 

 action rate will depend on the product of the length of encounter times 

 the number of encounters per second. One might hope that one could vary 

 the diffusion rate sufficiently to change from a diffusion independent rate 

 constant to a diffusion controlled constant. As will be seen later, one of the 

 reaction rate constants for our catalase satisfies this condition. 



CATALASE-HYDROGEN PEROXmE REACTION 



In discussing the reactions of catalase with hydrogen peroxide we have 

 used Chance's symbols (1). The reaction takes place in two steps: 



e — p X p 



cat + H2O2 , cat • H2O2 



P X 



cat • H2O2 + H2O2 — ^ cat + 2H2O + O2 



where the letters above the equations represent the concentrations of the 

 reactants. If x is sufficiently great compared to e - p, ko may be ignored. 

 Manipulating these algebraically, the concentrations should obey the 

 equations: 



^ = _ p (ki + k4) X + ki ex (/) 



dt 



^ = -k/ex (2^ 



dt 



where 



k.'= ' 



1/ki + l/k4 



In addition, p will reach a maximum pi , such that 



Reaction 1 may be observed at 405 m/i,, since the optical density of p is 

 less than e. Likewise pi/e may be determined at 405 m/x. On the other 

 hand, reaction 2 may be observed at 230 m/x where H2O2 has a stronger 

 absorption than the protein, catalase. 



