Catalase-alkyl hydroperoxide complexes

A striking difference between the primary alkyl hydroperoxide complexes and the primary hydrogen peroxide complex is that in the former all the catalase hematins are combined (Chance, 70). In the pH range 3.8-9.0 the combination follows the equation... 

Complexes of Catalase with Hydrogen Peroxide and Alkyl Hydroperoxides. 398... 

The conversion of the green primary complex into the pale red secondary complex appears to be a reduction process even though it occurs in the absence of any added hydrogen donors. The most definite evidence for this is the case of peroxidase where the speed of the conversion is increased in the presence of all compounds with which the peroxide system reacts (Chance, 55). For catalase, where the conversion can only be obtained with alkyl hydroperoxides, the evidence is not so clear-cut, but at least the velocity of formation of the secondary complexes increases as the hydroperoxide concentration is increased. An alternative explanation for these effects would be that the primary and secondary complexes are in some sort of equilibrium where removal of the latter would have the effect of increasing the rate of conversion. There is no indication of any such equilibrium, however, and direct reduction of the primary complex appears to be the most likely explanation. One possible formulation for this change involves the production of a ferryl ion type of compound by the removal of an OH radical by the hydrogen donor from the 02H anion bound to the iron atom ... 

Figure 6.3 Catalase redox transformation diagram. Compounds II, III and IV represent complexes of the enzyme with H202 and iron valence states, Fe5+, Fe4+ and Fe6+, respectively HXOH is a two-electron donor (reducer) X=0, NH, C=0, H(CH2) CH, where n = 1,2, 3 AH is a single-electron donor (reducer) ROOH is hydroperoxide (R is alkyl or acyl radical) and ROH is alcohol.

---