BRITTON CHANCE 



the Other hand, when an oxidizing agent other than peroxide 

 is used to form complex I, kinetic studies show definitely that 

 such agents do not react directly to form complex I. Never- 

 theless, the possibility of a two-step reaction of catalase or 

 peroxidase involving an intermediate preceding complex I 

 needs to be considered. 



THEORETICAL BACKGROUND 



By means of the accelerated-flow mediod we have observed 

 that complex I of catalase and hydrogen peroxide is the first 

 spectroscopically detectable intermediate to appear upon 

 addition of peroxide to catalase. And this is supported by the 

 fact that the pseudo first-order velocity constant for the forma- 

 tion of the complex has been found to increase linearly with 

 hydrogen peroxide concentration up to times as short as 2 milli- 

 sec. (Ref. 9, Figure 11). The second-order velocity constant 

 for the combination of catalase and hydrogen peroxide (0.4 X 

 10^ M~^ sec.~^ at 25° G.) agrees fairly well with the value 

 (0.6 X 10^ M~^ sec.~^) independently computed from the over- 

 all reaction (23). 



The velocity constant for the over-all reaction (k^) does not 

 depend solely upon the velocity constant for the formation of 

 complex I (ki), but it depends also upon the velocity constant 

 (^^4) for the reaction of complex I with the second peroxide 

 molecule, which serves as a hydrogen donor (23) : 



k[ = -y^ (1) 



_L _l_ _ 



A4 ni 



Nevertheless, the constancy of k[ with varying peroxide con- 

 centrations implies constancy of ^1 over this range. (Note 

 that if ki decreased while k[ remained constant, k^ would have 

 to increase. It is unlikely that the second-order velocity con- 

 stant would increase at high peroxide concentrations.) On 

 this basis experiments proving the constancy of k^^ from the 

 region of low peroxide concentrations where the kinetics of 



310 



