Oxidases, Peroxidases, and Catalase 



KURT G. STERN 



Yale University School of Medicine 



IN THIS PAPER no attempt will be made to treat the subject in a 

 comprehensive or systematic manner. A number of review ar- 

 ticles and monographs (4, 49, 50, 51, 62, 84, 85) have been written 

 on hemin catalysts and respiratory enzymes, to which the reader 

 is referred for information on historical developments, basic facts, 

 and details. By way of introduction some of the available data on 

 hemin catalyses and on hemin-containing enzymes are given in 

 Tables 1 to 5, which are documented by references to experimental 

 studies. 



The chief aims of this presentation are to bring out certain funda- 

 mental features shared by all the catalysts under discussion; to 

 analyze critically some of the controversial issues in the field; and to 

 trace some of the more recent developments. To conserve space 

 and to avoid overlappings with other papers, enzymes such as poly- 

 phenoloxidases, which contain copper rather than iron in their 

 prosthetic group, and the cytochromes, which cannot be regarded 

 as independent enzymes, will be considered only in so far as their 

 relationship to the hemin enzymes may require it. 



The Common Denominator in Hemin Catalyses 



All reactions and catalyses in which hemins participate are either 

 of the oxidative type or at least involve oxygen as a reactant. Under 

 this heading are grouped a variety of processes, ranging from the 

 transport of molecular oxygen by the respiratory pigments to the 

 activation of oxygen or the transfer of electrons from ferrous to ferric 

 iron. The few reports which have claimed that hemins or porphyrins 

 have promoted hydrolytic reactions remain unconfirmed. The pri- 

 mary step in many hemin catalyses appears to be an interaction be- 

 tween coordinatively linked, porphyrin-bound iron and the bond 

 between two oxygen atoms as it exists either in molecular oxygen 

 or in the forai of a peroxide bridge. This elementary process pre- 

 cedes or, indeed, represents what is mysteriously called the phe- 

 nomenon of "oxygen activation." All that we know about it is that 

 oxygen atoms thus captured acquire a state of high reactivity. The 



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