Peroxidase mammalian

Tomarev, S. I., et al. (1993). Abundant mRNAs in the squid light organ encode proteins with a high similarity to mammalian peroxidases. Gene 132 219-226. 

Nitric oxide is a physiological substrate for mammalian peroxidases [myeloperoxide (MPO), eosinophil peroxide, and lactoperoxide), which catalytically consume NO in the presence of hydrogen peroxide [60], On the other hand, NO does not affect the activity of xanthine oxidase while peroxynitrite inhibits it [61]. Nitric oxide suppresses the inactivation of CuZnSOD and NO synthase supposedly via the reaction with hydroxyl radicals [62,63]. On the other hand, SOD is able to modulate the nitrosation reactions of nitric oxide [64]. 

Furthermore, it was suggested that nitrite is a physiological substrate for mammalian peroxidases because it may compete with other physiological substrates (Cl-, Br, and SCN ) in the reactions catalyzed by MPO, EPO, and LPO. 

Abu-Soud, H. M., and Hazen, S. L., 2000, Nitric oxide is a physiological substrate for mammalian peroxidases, J. Biol. Chem. 275 31524-31532. 

The human body contains lactoperoxidase, a product of exocrine secretion into milk, saliva, tears, etc., and peroxidases with specialized functions in saliva, the thyroid, eosinophils,219 and neutrophils.220 The functions are largely protective but the enzymes also participate in biosynthesis. Mammalian peroxidases have heme covalently linked to the proteins, as indicated in Fig. 16-12 220 222a... 

Figure 16-12 Linkage of heme to mammalian peroxidases. There are two ester linkages to carboxylate side chains from the protein.220 221 Myeloperoxidase contains a third linkage.222 2223...

Zederbauer M, Furtmuller PG, Brogioni S et al (2007) Heme to protein linkages in mammalian peroxidases impact on spectroscopic, redox and catalytic properties. Nat Prod Rep 24 571-584... 

Huang LS, Wojciechowski G, Ortiz de Montellano PR (2006) Role of heme-protein covalent bonds in mammalian peroxidases - Protection of the heme by a single engineered heme-protein link in horseradish peroxidase. J Biol Chem 281 18983-18988... 

Compound I and Compound II) is required. The standard redox potential is then calculated from the Nemst equation. Errors in redox potentials estimated with this method may be in the order of 10 mV. This is the most commonly used method to determine redox potential of peroxidases [63, 66, 68, 69], and the redox agent is frequently K3hCl6 with E° = 0.93 V. However, it has been discussed that the species present in the equilibrium might not be equivalent to Compound I and Compound II formed in the presence of peroxide [100]. However, this drawback may be overcome in a recently reported modification of this method [64, 65]. By using stopped-flow spectrophotometry, it has been possible to utilize hydrogen peroxide as the redox agent, with errors of 3 mV or less. The redox potentials for mammalian peroxidases in Table 4.4 have been determined following this approach [65, 70, 71]. 

Pig. 5.9 Mechanism proposed for formation of a covalent bond between a heme methyl and a protein carboxyl group. A similar sequence must occur again to form the second heme-protein ester link in the mammalian peroxidases. In the heme structure, V stands for -CH=CH2 and P for... 

Heme modification by the products of peroxidase catalysis has been observed with peroxidases other than HRP, but it does not occur with all peroxidases. Some peroxidases are resistant to these types of reactions. In particular, the mammalian peroxidases are resistant to heme modification by both the free radical and electrophilic metabolites [63]. This resistance is due, at least in part, to the covalent bonds that link the heme to the mature protein. A similar resistance to modification by the HOBr produced by HRP is observed when the reaction is carried out with the F41E mutant in which a covalent bond to the heme has been introduced [65]. However, resistance to radical products can occur even without the presence of covalent links between the heme and the protein. Thus, LiP has a heme that is resistant to modification by phenylhydrazine or azide, although the protein is apparently inactivated by modifications of the protein [66]. 

Direct, two-electron oxidations are rare for most peroxidase enzymes. The one broad exception is the oxidation of halide and pseudohalide ions, specifically F, Br , Cl-, and NCS . Fluoride ion, in contrast, is not known to be oxidized by these enzymes. The oxidation of F and NCS" is common for the peroxidases, whereas that of Br is widespread but is usually less effective, and that of Cl , among the conventional peroxidases, is only important in the case of MPO [46, 83]. The halogenation activities of the mammalian peroxidases are compared in Table 5.3. As the table shows, chloride ion is oxidized by MPO, particularly at pH 5, but it is a very poor substrate for EPO and LPO. Br , F, and SCN" are readily oxidized by all three enzymes, but most efficiently by EPO at pH 5 [84—86]. 

Carpena X, Vidossich P, Schroettner K et al (2009) Essential role of proximal histidine-asparagine interaction in mammalian peroxidases. J Biol Chem 284 25929-25937... 

Colas C, Ortiz de Montellano PR (2004) Horseradish peroxidase mutants that autocataly-tically modify their prosthetic heme group. Insights into mammalian peroxidase heme-protein covalent bonds. J Biol Chem 279 24131-24140... 

Mammalian peroxidases Myeloperoxidase modified haem A (His) HOC1 formation 3.1.1.2. 

Mammalian peroxidases. Mammalian peroxidases [19] make up a separate peroxidase superfamily (not homologous to any of the enzymes in the previous section). They include proteins used for defence, such as myeloperoxidase [33], lactoperoxidase [34], salivary peroxidase [35] and eosinophil peroxidase [36], as well as those used for biosynthesis, such as thyroid peroxidase [37]. All these enzymes can oxidise halides and pseudohalides in vitro, the main difference being in the redox potential of compound I [38],... 

Most of the free radical metabolites formed by one-electron oxidation are formed by peroxidases (Table 2). The mechanism shown here is for horseradish peroxidase, which is also typical of the mammalian peroxidases (e.g., myeloperoxidase, lactoperoxidase, etc.). 

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