Catalase-peroxidase catalytic activity

Peroxidases and catalases contain high-spin Fe(III) and resemble metmyoglobin in properties. The enzymes are reducible to the Fe(II) state in which form they are able to combine (irreversibly) with 02. We see that the same active center found in myoglobin and hemoglobin is present but its chemistry has been modified by the proteins. The affinity for 02 has been altered drastically and a new group of catalytic activities for ferriheme-containing proteins has emerged. 

Myoglobin has the same prosthetic group as some peroxidases, such as horseradish peroxidase (HRP) or cytochrome c peroxidase, and reacts with H2O2 to produce a ferryl species, PFe(IV)=0, observed in the native peroxidase (see Iron Heme Proteins, Peroxidases, Catalases Catalase-peroxidases). However, the catalytic activity of myoglobin toward substrate oxidation is very low, because... 

The rate constants (Table 1.) for the peroxidase oxidation of phenol at various tenqreratures were calculated by the kinetic equation for a first order reaction (Fig.4). From the data in Table 1 is seen that on peroxidase oxidation of phenol, the catalase immobilized on "NORIT" soot shows a higher catalytic activity than the catalase in solution. It can be explained first, with the fact that the values in Table 1 are not the values for the specific rate constants, and secondly, as the catalase peroxidase fiuiction is characteristic of its subunits, with the complete or partial dissociation of catalase on its immobilization on "NORIT" soot. In this... 

The catalytic activity of co-ordination compounds in oxidations continues to be examined and, together with the Faraday Society Discussion, other aspects of this area of investigation have been the subject of recent reviews. Redox reactions involving bipyridyl and u-phenanthroline complexes of transition metals have been discussed and catalytic oxidations of complexes of manganese, cobalt, copper, and palladium have also been surveyed. Reviews are also available of ruthenium ammine chemistry, and redox reactions involving molybdenum complexes, together with an account of catalase and peroxidase reactivity of copper(ii) complexes. ... 

N—Fe(IV)Por complexes. Oxo iron(IV) porphyrin cation radical complexes, [O—Fe(IV)Por ], are important intermediates in oxygen atom transfer reactions. Compound I of the enzymes catalase and peroxidase have this formulation, as does the active intermediate in the catalytic cycle of cytochrome P Q. Similar intermediates are invoked in the extensively investigated hydroxylations and epoxidations of hydrocarbon substrates cataly2ed by iron porphyrins in the presence of such oxidizing agents as iodosylbenzene, NaOCl, peroxides, and air. 

At the same time the interaction of superoxide with MPO may affect a total superoxide production by phagocytes. Thus, the superoxide adduct of MPO (Compound III) is probably quantitatively formed in PMA-stimulated human neutrophils [223]. Edwards and Swan [224] proposed that superoxide production regulate the respiratory burst of stimulated human neutrophils. It has also been suggested that the interaction of superoxide with HRP, MPO, and LPO resulted in the formation of Compound III by a two-step reaction [225]. Superoxide is able to react relatively rapidly with peroxidases and their catalytic intermediates. For example, the rate constant for reaction of superoxide with Fe(III)MPO is equal to 1.1-2.1 x 1061 mol 1 s 1 [226], and the rate constants for the reactions of Oi and HOO with HRP Compound I are equal to 1.6 x 106 and 2.2 x 1081 mol-1 s-1, respectively [227]. Thus, peroxidases may change their functions, from acting as prooxidant enzymes and the catalysts of free radical processes, and acquire antioxidant catalase properties as shown for HRP [228] and MPO [229]. In this case catalase activity depends on the two-electron oxidation of hydrogen peroxide by Compound I. 

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