Irreversible Inhibition of Catalase 239 



Equation (7) may also be written in the following form: 



i = i^ + ^.i (8) 



X A7A5/2 k-jH i 



This expression (equation (8)) is identical with the one previously obtained 

 for the case in which the reaction mixture contained catalase, the irreversible 

 inhibitor and hydrogen peroxide but no catalase donor (Margohash and 

 Schejter, 1959). In the absence of donor and under experimental conditions 

 in which hydrogen peroxide is continuously supplied in excess, steady state 

 conditions may be assumed for the catalatic reaction and « is a constant 

 (Chance et al., 1952). However, when a donor is present in the reaction 

 mixture the concentration of Cat. U^O., I will vary with the concentration 

 and the rate of reaction of the donor with Cat. H2O2 1. Thus in the present 

 system, n in equation (8) could not be considered a constant and was defined 

 further. It should be noted, however, that for a particular concentration of 

 a specified donor and a particular concentration of hydrogen peroxide n will 

 remain constant, enabling /I to be measured under each set of experimental 

 conditions while the concentration of Cat. H2O2 I is constant. 



A kinetic equation for estimating the equilibrium constant for the reversible 

 reaction of an inhibitor with free catalase has been developed by Beers (1955); 

 applying it to reaction (c) gave : 



in which R^ is related to n by the expression (Beers, 1955): 



and AtqC and k^* are respectively the first order reaction constants for the 

 decomposition of hydrogen peroxide in the absence and in the presence of a 

 concentration of reversible inhibitor equal to /. Defining the factor 

 /A'o*/(Ao^ — Atq*) in equation (9) as K', equation (9) can be written: 



K, = K' ^"^ , (11) 



Substituting in equation (8) the value of n given by equation (10) one 

 obtains after suitable transformations : 



1 == J?^ + ^ + _L (12) 



A k^K^ k^i k^i 



