252 Discussion 



Per. H2O2 II. It will be slow because Per. HgOg II is not reduced rapidly by 

 H2O2 or donors such as alcohols. 



SUMMARY 



1. The need for limiting interaction between the normal and the doubly 

 oxidized state of the catalyst during decomposition of H2O2 by a 2-electron 

 mechanism leads to a consideration of the significance of bond-type in 

 determining the reaction paths. In the reactions of catalase and peroxidase 

 kinetic and steric barriers apparently co-operate with thermodynamic factors 

 to establish the rather limited specificity of the enzymes. 



2. Reasons are given for favouring a ferryl-type structure in the primary 

 catalase complex, as suggested by George (1952), and the possible nature of 

 the Fe — O bond is discussed, with preference for a form which may be 

 written Fe^^IO. 



Acknowledgement 



Dr. N. Ham and Dr. F. P. Dwyer are thanked for helpful advice. 



REFERENCES 



Beers, R. F., Jr. (1955). J.phys. Chem. 59, 25. 



Cahill, a. E. & Taube, H. (1951). /. Amer. chem. Soc. 73, 2847. 



Chance, B. (1951). The Enzymes, Vol. 2, Pt. 1, pp. 428-53. Ed. J. B. Sumner & K. 



Myrbiick. Academic Press Inc., New York. 

 Chance, B. & Fergusson, R. R. (1954). The Mechanism of Enzyme Action, pp. 389-98. 



Ed. W. D. McElroy & B. Glass. Johns Hopkins, Baltimore. 

 Chance, B., Greenstein, D., Higgins, J. & Yang, C. C. (1952). Arch. Biochem. Biophys. 



yi, 322. 

 Dwyer, F. P., King, N. K. & Winfield, M. E. (1959). Aust. J. Chem. 12, 138. 

 Fergusson, R. R. (1956). /. Amer. chem. Soc. 78, 741. 

 George, P. (1952). Advances in Catalysis, 4, pp. 367-428. Ed. W. G. Frankenburg, V. I. 



Komarewsky & E. K. Rideal. Academic Press Inc., New York. 

 Gibson, J. F. & Ingram, D. J. E. (1956). Nature, Lond. 178, 871. 

 Gibson, J. F., Ingram, D. J. E. & Nicholls, P. (1958). Nature, Lond. 181, 1398. 

 Keilin, D. & Hartree, E. F. (1951). Biochem. J. 49, 88. 

 King, N. K. & Winfield, M. E. (1959a). Aust. J. Chem. 12, 47. 

 King, N. K. & Winfield, M. E. (1959b). Aust. J. Chem. 12, 147. 

 Theorell, H. & Ehrenberg, a. (1952). Arch. Biochem. 41, 442. 



Werner, A. (191 1). A^^vi' Ideas on Inorganic Chemistry. London : Longmans, Green & Co. 

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DISCUSSION 



Oxidation States of Haemoproteins 



George: I think there is now a substantial body of evidence to show that the compounds 

 which are formed when ferrimyoglobin, ferrihaemoglobin, ferriperoxidase and ferri- 

 catalase react with strong oxidizing agents are higher oxidation states of the prosthetic 

 group, that can be formally represented as Fe^^' and Fe^' derivatives. Compounds 

 of this type were suggested as the reactive intermediates in systems containing iron 

 salts and hydrogen peroxide at least fifty years ago; but, although Polonovski, Jayle, 

 Glotz and Fraudet proposed their participation in haemoprotein reactions in a series 

 of papers from 1939 to 1941, systematic experimental studies to demonstrate the one 

 and two equivalent oxidation steps, and to distinguish between some of the structures 

 that are possible, have only been carried out over the last ten years. 



