CATALASE OXIDATION MECHANISMS 



By M. E. WiNFIELD 



Division of Physical Chemistry, C.S.I.R.O. Chemical Research 

 Laboratories, Melbourne 



INTRODUCTION 

 Chance and Fergusson (1954) have proposed that the catalatic cycle consists 



^^'' Fe-HOH + HgOo^ FeHOOH + HgO (1) 



Catalase Cat. H^G^ I 



FeHOOH^ Fe-HOH + H2O + O2 (2) 



J \ Catalase 



+ HOOH 



Contrary to the behaviour of the majority of catalysts for HgOg decomposi- 

 tion, catalase does not appear to function by 1 -electron steps. In reaction (2) 

 both reducing equivalents of the H2O2 donor molecule are transferred to 

 the catalase peroxide compound I (Cat. H2O2 1) in a single step, in the sense 

 that no intermediates can be detected by the most rapid means available. If 

 intermediates do occur, their lifetime must be less than 10~'^ sec (Chance and 

 Fergusson, 1954) and we can assume for practical purposes that the two 

 equivalents are transferred simultaneously. 



The scheme shown above is in accord with much of a large body of evidence 

 obtained by kinetic, titrimetric, isotopic and other studies. To go further, 

 and try to show in some detail the way in which reactions (1) and (2) take 

 place, is to move into the realm of speculation, where it is necessary to draw 

 upon analogies to the reactions of other co-ordination complexes, and on 

 processes of elimination. King and Winfield (1959a) have discussed the 

 merits of several possible structures for catalase complexes, and Dwyer 

 et al. (1959) have attempted to show that 2-electron mechanisms for the 

 oxidation and reduction of H2O2 might be achieved with non-enzymic 

 catalysts which have certain closely defined oxidation potentials, together 

 with some means for limiting interaction between the oxidized and reduced 

 forms of the catalyst. In the present paper we wish to indicate more clearly 

 where our views on the catalytic mechanism are in harmony with those of 

 Chance, and a few respects in which they differ. 



Valency Changes DISCUSSION 



Catalase contains four iron-porphyrin groups. It is convenient however to 

 refer to one iron atom when describing most of the reactions of the enzyme. 



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