438 IX. HEMATIN ENZYMES, II 



The following theory appears to be in better accordance with the 

 known facts (Fig. 5). 



in 



O2 + HjM H2O2 +M 



Fe'+OH 



+ HjM 

 Fe«+OH 



[2] 

 H2M 



+ H1O2 [ 3 



Fe'+OjH 



—^ — 



[4] 

 ^e'"" + H2O2 + HM 



[5l/ N^^ > 2H2O + M 



^+0, [91 \ 



Fe-02 Fe«-H202 ^^^ 



-H- 



(61 [81+ HjM 



Fe2+ •H2O2 



[n . 1 ,. +M 



^r°' H,M ,„ r*»*' 



•M- 



Fig. 5. Mechanism of action of dihydroxymaleic acid oxidase. 



Step 1. The reaction begins with the autoxidation of dihydroxymaleic 

 acid, which provides the hydrogen peroxide required for the initiation of the 

 reaction. If catalase is present this is destroyed and no catalysis takes place. 



Steps 2 and 3. Hydrogen peroxide and dihydroxymaleic acid unite with 

 the peroxidase to a complex. 



Step If.. Unlike the normal peroxidative reaction which leads back to 

 ferric peroxidase, the ferric iron in the hydrogen peroxide ferriperoxidase is 

 reduced by the' dihydroxymaleic acid. It is assumed that this reaction does 

 not take place in the ferriperoxidase -dihydroxymaleic acid complex without 

 the peroxide bound to the iron. The hydrogen peroxide may be liberated, 

 or, more likely, dispo.sed of in a peroxidative reaction with a second molecule 

 of dihydroxymaleic acid. 



