Peroxidases heme-containing enzyme

The direct interactions between metals and ONOO- can catalyze modifications. For example, the metals in Cu,Zn SOD and FeEDTA (EDTA = ethyl-enediaminetetraacetic acid) enhance nitration reactions (229). Heme-containing enzymes such as myeloperoxidase (6 x 106A/-1 s-1) and lactoperoxidase (3.3 x 105M-1s-1) also react with ONOO- (230) such that compound II [FeIV(P+)0] is formed. In contrast, horseradish peroxidase (3.2 x 106M-1 s-1) is converted to compound I (FevO) by ONOO-. Floris et al. (230) proposed an interesting mechanism by which compound I is initially produced and then rapidly oxidizes NO-f to N02. In the presence of NO, a number of nitrosation reactions would subsequently be facilitated by subsequent formation of N2O3 (Eq. 32). 

Alternative b is the most probable for cytochrome-c-peroxidase complex. Here, the N2 atom is the basic site of the catalytic act (which promotes specificity of the cytochrome-c-peroxidase complex) and the proton donor, simultaneously. It should be noted that in other heme-containing enzymes N2 atom of His 552 (fragment a) may be of the amphoteric type. 

The heme-containing enzymes catalase and peroxidase are responsible for the removal of long-lived H202 according to the following reactions ... 

Peroxidases fall into two superfamilies (plant and mammalian) and a third, indistinct group that includes chloroperoxidase (a P450-like hybrid) and di-heme cytochrome c peroxidase from Pseudomonas aeruginosa. The plant peroxidase superfamily contains enzymes of plant, fungal, and bacterial origin [126], Mammalian peroxidases make up the second superfamily, and include lactoperoxidase, myeloperoxidase, and prostaglandin H synthase. Both families have been the focus of numerous excellent reviews, several of which have discussed the differences between the plant and mammalian peroxidases [126-130], Here, recent experimental investigations focused on the plant peroxidases will be discussed. 

Peroxidases (EC 1.11.1.7 hydrogen donor H2O2 oxidoreductase) are heme-containing enzymes, which catalyze the single one-electron oxidation of several substrates at the expense of H2O2 ... 

Is lipid-assisted folding a widespread phenomenon and possibly applicable to soluble proteins The erythrocyte membrane contains about 20-mole % of PE that is almost exclusively localized in the inner leaflet and is in contact with highly concentrated heme-containing proteins. The refolding of the denatured soluble and heme-containing enzyme horseradish peroxidase (HRP) was followed in the presence and absence of liposomes made up of different phospholipids (Debnath et al., 2003). Remarkably, dimyristoyl-PE (a bilayer-forming... 

Oxidation and Iodination. The oxidation of iodide to its active form and the iodination of tyrosine are catalyzed by thyroid peroxidase, a heme-containing enzyme that utilizes hydrogen peroxide (HjOj) as the oxidant. The peroxidase is membrane-bound and concentrated at the apical surface of the thyroid cells. The reaction forms mono- and diiodotyrosyl residues in thyroglobulin just prior to its extracellular storage in the lumen of the thyroid follicle. is formed near its site of utilization and is stimulated by a rise in cytosolic Cd . ... 

Axial ligands of heme-containing enzymes, such as a cysteine thiolate in cytochromes P450 and chloroperoxidases, a histidine imidazole in peroxidases, and a tyrosine phenolate in catalases, are... 

Electrochemical properties of this heme-containing enzyme have been studied. The potentiodynamic curves measured on the gold amalgamated electrode in the presence of peroxidase in the electrolyte show two maxima— anodic and cathodic (Figure 9), near the potential E 0.10 V. Replacement of the test electrolyte with electrolyte containing no peroxidase did not lead to a change in the variation of charging curves. This points to the irreversible... 

The phenoloxidases are a related group of copper containing enzymes that catalyze the oxidation of phenols to quinones in animals and plants (5,6). Two distinct types of phenoloxidases that have substrate specificities and inhibitor sensitivities resembling typical tyrosinases and laccases are found in different types of insect cuticle (Z 8). Peroxidases, heme-containing enz)niies that also oxidize diphenols to quinones, may be present in cuticle and may play a role in sclerotization (9,10). 

Peroxidases catalyze the two-electron reduction of H2O2 (or organic peroxides) to H2O (or alcohols) by electron-transfer proteins or small organic reagents. A general catalytic cycle for the heme-containing enzymes is shown in Scheme 7. 

Peroxidases (E.C. 1.11.1.7) are ubiquitously found in plants, microorganisms and animals. They are either named after their sources, for example, horseradish peroxidase and lacto- or myeloperoxidase, or akin to their substrates, such as cytochrome c, chloro- or lignin peroxidases. Most of the peroxidases studied so far are heme enzymes with ferric protoporphyrin IX (protoheme) as the prosthetic group (Fig. 1). However, the active centers of some peroxidases also contain selenium (glutathione peroxidase) [7], vanadium (bromoperoxidase)... 

Heme coenzymes (8) with redox functions exist in the respiratory chain (see p. 140), in photosynthesis (see p. 128), and in monooxygenases and peroxidases (see p. 24). Heme-containing proteins with redox functions are also referred to as cytochromes. In cytochromes, in contrast to hemoglobin and myoglobin, the iron changes its valence (usually between +2 and +3). There are several classes of heme (a, b, and c), which have different types of substituent - Ri to - R 3. Hemoglobin, myoglobin, and the heme enzymes contain heme b. Two types of heme a are found in cytochrome c oxidase (see p. 132), while heme c mainly occurs in cytochrome c, where it is covalently bound with cysteine residues of the protein part via thioester bonds. 

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