Hydrogen peroxide-catalase complexes

Fig. 10. The formation of hydrogen peroxide-catalase complex II in the hydroxylating mixture of Udenfriend. Catalase 5.4 x 10 mM 20 mM ascorbate 0.33 mM FeSO 6.66 mM versene 1.66 mM phosphate buffer pH 6.8. The second spectrum was recorded after 15 minutes of oxygenation. Spectrophotometer Beckman DK 1. From Zito and Kertesz (1962).

Fig. 12. Formation of the Soret band of the hydrogen peroxide-catalase complex II during the oxidation of ascorbic acid by the phenolase plus o-dihydroxyphenol system (compare with Fig. 4 of Chance, 1950) and its disappearance after the addition of a monohydroxyphenol. (1) Catalase 0.9 x 10 mAf 3.1 X 10 mM phenolase 5 x 10 mM catechol 20 vaM ascorbate 1.66 mM phosphate buffer pH 6.8 total volume 3 ml. (2) the same after 15 minutes of oxygenation and (3) immediately after the addition of 1 /tmole of phenol in 0.005 ml. The lower curves are the spectra of the controls without catalase. Spectrophotometer Beckman DK 1. From Zito and Kertesz (1961).

Catalase (EC 1.11.1.6) rapidly formed a reversible complex stoichiometrically with nitric oxide with the Soret band shifting from 406 to 426 nm and two new peaks appeared at 540 and at 575 nm, consistent with the formation of a ferrous-nitrosyl complex (Brunelli et al. 2001). Catalase consumed more nitric oxide upon the addition of hydrogen peroxide. Conversely, micromolar concentrations of nitric oxide slowed the catalase-mediated decomposition of hydrogen peroxide. Catalase pre-treated with nitric oxide and hydrogen peroxide regained full activity after dialysis. 

Heme (C34H3204N4Fe) represents an iron-porphyrin complex that has a protoporphyrin nucleus. Many important proteins contain heme as a prosthetic group. Hemoglobin is the quantitatively most important hemoprotein. Others are cytochromes (present in the mitochondria and the endoplasmic reticulum), catalase and peroxidase (that react with hydrogen peroxide), soluble guanylyl cyclase (that converts guanosine triphosphate, GTP, to the signaling molecule 3, 5 -cyclic GMP) and NO synthases. 

How does nature prevent the release of hydrogen peroxide during the cytochrome oxidase-mediated four-electron reduction of dioxygen It would appear that cytochrome oxidase behaves in the same manner as other heme proteins which utilize hydrogen peroxide, such as catalase and peroxidase (vide infra), in that once a ferric peroxide complex is formed the oxygen-oxygen bond is broken with the release of water and the formation of an oxo iron(IV) complex which is subsequently reduced to the ferrous aquo state (12). Indeed, this same sequence of events accounts for the means by which oxygen is activated by cytochromes P-450. 

Answers to these questions were initiated over a decade ago during our studies on catalase (CAT) and horseradish peroxidase (HRP) (30). Both native enzymes are ferric hemoproteins and both are oxidized by hydrogen peroxide. These oxidations cause the loss of two electrons and generate active enzymatic intermediates that can be formally considered as Fe + complexes. 

Fig. 2. The Bonnichsen, Chance, and Theorell 34) mechanism for the dismutation of hydrogen peroxide by catalase. (A) The simple ping-pong mechanism (ferric-peroxide compound (ycle) involves only the successive formation and decomposition of the compound 1 intermediate by two successive molecules of H2O2. (B) Reversible ES(Fe -H202) and ternary (compound I-H2O2]) complexes are added to the mechanism in A.

In part motivated by the desire to model biological redox processes, there have been many studies in which Robson-type macrocycles (205) (R = H) have been employed to form dinuclear manganese species.For example, a novel macrocyclic heterodinuclear catalase-like model complex of type (206) has been reported. " This complex can dismute hydrogen peroxide to dioxygen in basic aqueous solution. 

The dibenzotetraaza[14]annulene-iron(III) cation (144) shows catalase-like activity, converting hydrogen peroxide into dioxygen under physiological conditions. The iron(II) complex of... 

III) form of Lactobacillus plantarum is depicted in Fig. 13 [105,106]. The Mn centers are bridged by oxo, hydroxo, and car-boxylato ligands in a manner similar to the binuclear structures (8-10) in Sect. 16.1.4. A proposed mechanism for hydrogen peroxide dismutation by Mn catalase is presented in Fig. 14. A number of model studies of H2O2 disproportionation employing bridged binuclear Mn complexes have been conducted [107]. 

SCHEME 4.3 Cytochrome P450 and peroxidase pathways to hydroperoxo-ferric intermediate or Compound 0 (5). Ferric cytochrome P450 (1) is reduced to the ferrous state (2), which can hind dioxygen to form oxy-ferrous complex (3). Reduction of this complex results in the formation of peroxo-ferric complex (4), which is protonated to give hydroperoxo-ferric complex (5). The same hydroperoxo-ferric complex is formed in peroxidases and catalases via reaction with hydrogen peroxide. 

If the diagram is analyzed in the context of the principles of conjugated reaction, it may be concluded that conjugated biooxidation with hydrogen peroxide consists of the basic (primary) catalase reaction of H202 dissociation (reaction (6.17)). Owing to the Chance complex formation [116, 117], this primary reaction induces the secondary non-classical peroxidase reaction (6.18). 

Moreover, when 02 is formed in the hydrophobic stage, vitamin E (20, tocopherol) creates a hydrogen atom. The hydrogen peroxide formed is decomposed to water and molecular oxygen catalyzed by catalase enzyme (protein containing Fe-complex), and the oxidized vitamin E radical is reduced to vitamin E again by vitamin C (eq. 1.10)... 

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