ANTICATALASES AND PHILOCATALASES 



443 



Since the transformation of hydrogen peroxide into oxygen involves 

 a dehydrogenation of hydrogen peroxide, and since the specific 

 protein is obviously of fundamental importance, a dehydrogenating 

 group (X) is assumed in the protein part of the catalase molecule. 

 The action of catalase in the absence of reducing substances or azide 

 is assumed to proceed as shown in Figure 6, without valency change 

 of the iron. 



Fe'+OH 



+ 2H2O 



+ H2O 



+ O2 

 Fig. 6. Assumed mode of action of catalase. 



Step 1 is formulated as by Sumner and Theorell. 



Step 2 represents the rapid break-down of the catalase-hydrogen peroxide 

 compound with liberation of oxygen. The hydrogen peroxide is dehydro- 

 genated to oxygen by the specific hydrogen acceptor group X of the protein. 

 The presence of this group in catalase and its absence in other hemoproteins 

 would explain the lack of catalase activity of the latter. This type of intra- 

 complex reaction can be assumed to be more rapid than the bimolecular 

 reaction assumed as step '■2 in Sumner's theory. 



Step 3. Finally the active catalyst is restored, by oxidation of the XH2 

 group by a second molecule of hydrogen peroxide. 



It would be premature to make special assumptions about the nature of 

 the hydrogen acceptor group, X, in the catalase protein. It may be men- 

 tioned that catalase is not inhibited by iodoacetic acid (Barron and Singer, 

 IS!)); this was confirmed by Lemberg and Foulkes {1699).* 



4.2.5. Anticatalases and Philocatalases. In Section 2.4. we have 

 seen that some reducing substances, such as sulfhydryl compounds 

 and ascorbic acid, cause an apparent inhibition of catalase which is 

 actually due to irreversible destruction of the enzyme. They thus 



* Cf. also Gordon and Quastel {1023a), Barron and co-workers {18-3a); cf., however. 

 Cook and co-workers {iS5a). 



