PHILIP GEORGE 



energy change would then favor the following reaction between 

 the two couples 



FeJer + Fe^pt(H,0) ^=^ IFcZ (9) 



in the forward direction at high pH values and in the reverse 

 direction at low/^H values. On the other hand, if the structures 

 of compounds I and II are such that the two single equivalent 

 reduction steps are the same, i.e., H-atom transfer or its equiva- 

 lent (electron transfer and H ^ association), the respective oxida- 

 tion-reduction potentials would show the same pH variation. 

 These stability relationships would then have to be explained 

 either through the operation of heme-linked ionizations alone, 

 or by postulating that the speed of reduction of compound I to 

 compound II is less in more acid solution, which seems very 

 unlikely. 



Finally, the observation that other strong oxidizing agents 

 as well as peroxides form the higher oxidation states can be seen 

 to have a very important bearing upon biological oxidation. 

 The appearance of these compounds in intact enzyme systems 

 in vivo can no longer be taken as proof that hydrogen peroxide is 

 formed as such during the reduction of oxygen to water, which 

 provides the driving force for the oxidation process (4). It just 

 remains a very likely possibility. 



Conclusions 



As more and more data have accumulated, it appears that 

 hemoprotein structures and reactions can be interpreted in 

 terms of the present system of chemical and physical theory. 

 There is no compelling evidence, from the in vitro reactions 

 which have been thoroughly investigated to suggest that funda- 

 mentally new properties emerge at this level of molecular 

 complexity, or that fundamentally new principles need be 

 invoked to explain the reactions. Whilst it is true that the 

 especially complicated hemoprotein structure endows individual 

 hemoproteins with a reactivity that is shared by others to a far 



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