Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:1.11.1.7 (peroxidase)
65,474 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The quenching of the Y(D)(.) tyrosyl radical in photosystem II by nitric oxide was reported to result from the formation of a weak tyrosyl radical-nitric oxide complex (Petrouleas, V., and Diner, B. A. (1990) Biochim. Biophys. Acta 1015, 131-140). This radical/radical reaction is expected to generate an electron spin resonance (ESR)-silent 3-nitrosocyclohexadienone species that can reversibly regenerate the tyrosyl radical and nitric oxide or undergo rearrangement to form 3-nitrosotyrosine. It has been proposed that 3-nitrosotyrosine can be oxidized by one electron to form the tyrosine iminoxyl radical (>C=N-O*). This proposal was put forth as a result of ESR detection of the iminoxyl radical intermediate when photosystem II was exposed to nitric oxide (Sanakis, Y., Goussias, C., Mason, R. P., and Petrouleas, V. (1997) Biochemistry 36, 1411-1417). A similar iminoxyl radical was detected in prostaglandin H synthase-2 (Gunther, M. R., Hsi, L. C., Curtis, J. F., Gierse, J. K., Marnett, L. J., Eling, T. E., and Mason, R. P. (1997) J. Biol. Chem., 272, 17086-17090). Although the iminoxyl radicals detected in the photosystem II and prostaglandin H synthase-2 systems strongly suggest a mechanism involving 3-nitrosotyrosine, the iminoxyl radical ESR spectrum was not unequivocally identified as originating from tyrosine. We report here the detection of the non-protein L-tyrosine iminoxyl radical generated by two methods: 1) peroxidase oxidation of synthetic 3-nitroso-N-acetyl-L-tyrosine and 2) peroxidase oxidation of free L-tyrosine in the presence of nitric oxide. A newly developed ESR technique that uses immobilized enzyme was used to perform the ESR experiments. Analysis of the high resolution ESR spectrum of the tyrosine iminoxyl radical generated from free tyrosine and nitric oxide reveals a 28.4-G isotropic nitrogen hyperfine coupling and a 2.2-G proton hyperfine coupling assigned to the proton originally ortho to the phenoxyl oxygen.
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PMID:Tyrosine iminoxyl radical formation from tyrosyl radical/nitric oxide and nitrosotyrosine. 1155 49

The quenching of the Y(D) tyrosyl radical in photosystem II by nitric oxide was reported to result from the formation of a weak tyrosyl radical-nitric oxide complex. This radical/radical reaction is expected to generate an electron spin resonance (ESR)-silent nitrosocyclohexadienone species that can reversibly regenerate the tyrosyl radical and nitric oxide or undergo rearrangement to form 3-nitrosotyrosine. It has been proposed that 3-nitrosotyrosine can be oxidized by one electron to form the tyrosine iminoxyl radical (>C=N-O.). This proposal was put forth as a result of ESR detection of the iminoxyl radical intermediate when photosystem II was exposed to nitric oxide. Although the detection of the iminoxyl radical in photosystem II strongly suggested a mechanism involving 3-nitrosotyrosine, the iminoxyl radical ESR spectrum was not unequivocally identified as originating from tyrosine. Subsequently, non-protein L-tyrosine iminoxyl radical was generated by two methods: (1) peroxidase oxidation of synthetic 3-nitroso-N-acetyl-L-tyrosine; and (2) peroxidase oxidation of free L-tyrosine in the presence of nitric oxide. The determination of protein nitrotyrosine content has become a frequently used technique for the detection of nitrosative tissue damage. Protein nitration has been suggested to be a final product of the production of highly reactive nitrogen oxide intermediates (e.g. peroxynitrite) formed in reactions between nitric oxide (NO.) and oxygen-derived species such as superoxide. The enzyme prostaglandin H synthase-2 also forms a tyrosyl radical during its enzymatic catalysis of prostaglandin formation. In the presence of the NO.-generator diethylamine nonoate, the tyrosyl radical of prostaglandin H synthase-2 also changes to that of an iminoxyl radical. Western blot analysis of prostaglandin H synthase-2 after exposure to the NO.-generator revealed nitrotyrosine formation. The results provide a mechanism for nitric oxide-dependent tyrosine nitration that does not require formation of more highly reactive nitrogen oxide intermediates such as peroxynitrite or nitrogen dioxide.
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PMID:Nitric oxide trapping of the tyrosyl radical-chemistry and biochemistry. 1212 91

To kill invading bacteria, viruses, and fungi, phagocytes secrete hydrogen peroxide (H(2)O(2)) and the heme enzyme myeloperoxidase. We have explored the possibility that myeloperoxidase might use H(2)O(2) to convert L-tyrosine to tyrosyl radical. Activated human neutrophils and monocytes used the system to oxidize free L-tyrosine to o,o'-dityrosine, a stable product of tyrosyl radical. Protein-bound tyrosyl residues exposed to myeloperoxidase, H(2)O(2), and L-tyrosine were also oxidized to o,o'-dityrosine. The cross-linking reaction required free L-tyrosine, suggesting that myeloperoxidase converts the amino acid to a diffusible radical catalyst that promotes protein oxidation. We used electron paramagnetic resonance to provide direct evidence that the oxidizing intermediate is free tyrosyl radical. Myeloperoxidase-generated tyrosyl radical also initiates lipid peroxidation, suggesting that activated phagocytes might also be able to oxidize lipids in host tissues. Moreover, myeloperoxidase is present and active in human atherosclerotic tissue, and levels of protein-bound dityrosine are elevated in such lesions. Our recent studies indicate that activated neutrophils use oxidants generated by the phagocyte NADPH oxidase to produce protein-bound dityrosine during acute inflammation. Collectively, these findings suggest that generation of tyrosyl radical by myeloperoxidase allows activated phagocytes to damage both proteins and lipids. Elevated levels of o,o'-dityrosine have been detected in inflammatory lung disease, neurodegenerative disorders, and aging. Thus, oxidation of tyrosine to tyrosyl radical might play a role in the pathogenesis of many diseases.
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PMID:Tyrosyl radical production by myeloperoxidase: a phagocyte pathway for lipid peroxidation and dityrosine cross-linking of proteins. 1212 92

Peroxidase/H2O2/phenothiazine systems irreversibly inhibit Trypanosoma cruzi dihydrolipoamide dehydrogenase (LADH). Inactivation of the parasite enzyme depended on (a) phenothiazine structure; (b) peroxidase nature; (c) incubation time and (d) the presence of a cation radical scavenger. With the myeloperoxidase/H2O2/system, promazine, trimeprazine, thioridazine, promethiazine, prochlorperazine, chlorpromazine and perphenazine were the most effective derivatives out of twelve phenothiazines studied. An electronegative substituent at position 2 of the phenothiazine ring such as Cl, or trifluoromethyl, propionyl and nitrile groups decreased or nullified phenothiazine activity. Myeloperoxidase/H2O2/, horseradish peroxidase/H2O2/, and myoglobin/H2O2/systems activated phenothiazines producing the corresponding cation radicals, myeloperoxidase being the most selective one with respect to phenothiazine structure. The myoglobin/H2O2/system activated phenothiazines that were scarcely active or inactivate with the MPO/H2O2/system, such as the trifluoromethyl derivatives. Production of phenothiazine cation radicals was demonstrated by optical spectroscopy. Phenothiazine cation radical stability depended on their structure as illustrated by promazine and thioridazine. Thiol compounds (GSH, N-acetyl-cysteine and penicillamine), aromatic aminoacids (L-tyrosine, L-tryptophan, and the corresponding peptides) and ascorbate scavenged phenothiazine cation radicals, thus preventing LADH inactivation. Comparison of the summarized phenothiazine effects with those of phenothiazines on T. cruzi suggest the role of cation radicals in phenothiazines chemotherapeutic actions.
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PMID:Myeloperoxidase-generated phenothiazine cation radicals inactivate Trypanosoma cruzi dihydrolipoamide dehydrogenase. 1218 Feb 62

Immunohistochemical artifacts for nitrotyrosine were investigated in eosinophils with regard to fixatives. Immunoreactivity for nitrotyrosine was revealed in separated eosinophils and in gastric mucosa fixed with periodate, lysine-paraformaldehyde (PLP). The increase in immunoreactivity by PLP was due to periodate itself, a component of PLP. Nitrotyrosine formed by peroxidase using NO2- and H2O2 or by peroxynitrite was not completely inhibited by 100 mM dithionite but the immunoreactivity for nitrotyrosine antibodies by PLP was completely inhibited by 5.7 mM dithionite. Although untreated eosinophils or ovalbumin (OVA) did not show protein tyrosine nitration in a standard Western blot, the treatment of the blotted membrane with PLP increased the reactivities of proteins from eosinophils with anti-nitrotyrosine antibodies. The increase in immunoreactivity of OVA with anti-nitrotyrosine antibodies by PLP did not change with pre-treatment with dithionite but was abolished by treatment with dithionite after PLP fixation. In HPLC assays, periodate did not generate nitrotyrosine from L-tyrosine and aminotyrosine. These results suggest that the treatment of eosinophils or eosinophil-containing tissues with PLP fixative augments the immunoreactivity of nitrotyrosine antibodies with eosinophils due to the formation of epitopes similar to nitrotyrosine by an oxidation reaction of periodate, which evokes an artifact in nitrotyrosine immunohistochemistry.
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PMID:Immunohistochemical artifact for nitrotyrosine in eosinophils or eosinophil containing tissue. 1259 68

Phenothiazine cation radicals (PTZ+*) irreversibly inactivated Trypanosoma cruzi dihydrolipoamide dehydrogenase (LADH). These radicals were obtained by phenothiazine (PTZ) peroxidation with myeloperoxidase (MPO) or horseradish peroxidase (HRP/H2O2) systems. LADH inactivation depended on PTZ structure and incubation time. After 10 min incubation of LADH with the MPO-dependent systems, promazine, trimeprazine and thioridazine were the most effective; after 30 min incubation, chlorpromazine, prochlorperazine and promethazine were similarly effective. HRP-dependent systems were equally or more effective than the corresponding MPO-dependent ones. Chloro, trifluoro, propionyl and nitrile groups at position 2 of the PTZ ring significantly decreased molecular activity, specially with the MPO/H2O2 systems. Comparison of inactivation values for LADH and T. cruzi trypanothione reductase demonstrated a greater sensitivity of LADH to chlorpromazine and perphenazine and a 10-fold lower sensitivity to promazine, thioridazine and trimeprazine. Alkylamino, alkyl-piperidinyl or alkyl-piperazinyl groups at position 10 modulated PTZ activity to a limited degree. Production of PTZ+* radicals was demonstrated by optical and ESR spectroscopy methods. PTZ+* radicals stability depended on their structure as demonstrated by promazine and thioridazine radicals. Thiol compounds such as GSH and N-acetylcysteine, L-tyrosine, L-tryptophan, the corresponding peptides, ascorbate and Trolox, prevented LADH inactivation by the MPO/H2O2/thioridazine system, in close agreement with their action as PTZ+* scavengers. NADH (not NAD+) produced transient protection of LADH against thioridazine and promazine radicals, the protection kinetics being affected by the relatively fast rate of NADH oxidation by these radicals. The role of the observed effects of PTZ radicals for PTZ cytotoxicity is discussed.
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PMID:Phenothiazine radicals inactivate Trypanosoma cruzi dihydrolipoamide dehydrogenase: enzyme protection by radical scavengers. 1268 23

We have developed an in vitro assay system for the evaluation of the inhibitory effects of phenolic antioxidants on myeloperoxidase (MPO) activity. The formation of dityrosine from the MPO/H2O2/L-tyrosine system was used as an indicator of the MPO activity. Because the buffer system used does not include chloride ion, this assay has the advantage of exclusion of direct reaction between an antioxidant and HOCl. In this assay, ferulic acid, gallic acid, and quercetin strongly inhibited the dityrosine formation, and curcumin and caffeic acid were also effective.
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PMID:Inhibition of myeloperoxidase-catalyzed tyrosylation by phenolic antioxidants in vitro. 1283 95

Proteins are targets of reactive nitrogen species such as peroxynitrite and nitrogen dioxide. Among the various amino acids in proteins, tryptophan residues are especially susceptible to attack by reactive nitrogen species. We carried out experiments on the reactions of peroxynitrite and other reactive nitrogen species with N-acetyl-L-tryptophan under various conditions. Four major products were identified as 1-nitroso-N-acetyl-L-tryptophan, 1-nitro-N-acetyl-L-tryptophan, 6-nitro-N-acetyl-L-tryptophan, and N-acetyl-N'-formyl-L-kynurenine on the basis of their mass and UV spectra. The reactions with SIN-1 (a peroxynitrite generator), Angeli's salt (a nitroxyl donor), and spermine NONOate (a nitric oxide donor) generated the nitroso derivative but not the nitro derivatives. A myeloperoxidase-H(2)O(2)-NO(2)(-) system generated the nitro derivatives but not the nitroso derivative. Under physiological conditions 6-nitro-N-acetyl-L-tryptophan was stable, whereas the 1-nitroso and 1-nitro derivatives decomposed with half-lives of 1.5 and 18 h, respectively. After treatment with various reactive nitrogen species, bovine serum albumin was enzymatically hydrolyzed and analyzed for 6-nitro-L-tryptophan and 3-nitro-L-tyrosine by HPLC with electrochemical detection. Levels of 6-nitro-L-tryptophan and 3-nitro-L-tyrosine were similar in the nitrated protein. 6-Nitro-L-tryptophan in proteins can be measured as an additional biomarker of protein nitration.
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PMID:Nitration and nitrosation of N-acetyl-L-tryptophan and tryptophan residues in proteins by various reactive nitrogen species. 1528 24

Previously, we have shown that the amphiphilic decyl esters of both D- and L-tyrosine (DELT) self-assemble in aqueous solution above their critical micelle concentration values to form long rodlike structures that can be enzymatically polymerized. In the current study, we have examined the self-assembled structures of unpolymerized and enzymatically (horseradish peroxidase) copolymerized 1:1 molar mixtures of DELT with the nonamphiphilic comonomer L-tyrosineamide. The structures were examined following adsorption to gold-coated mica surfaces using optical microscopy and scanning electron microscopy, but primarily noncontact atomic force microscopy. Both unpolymerized and copolymerized 1:1 comonomer mixture aggregates produced amorphous to spherical shaped structures, exhibiting increased flexibility that contrasted with our previous observations of the more highly ordered long rodlike structures seen with the pure DELT. The unpolymerized comonomer aggregates were amorphous and of varying size. Interestingly, they contained occasional novel structures-smooth, sharp, nipplelike features that rose hundreds of nanometers above the smooth aggregate surface. However, upon enzymatic copolymerization, the structures are altered, forming nearly hemispherical aggregates in contact with each other on the surface. These structures possessed diameters of 1.51 +/- 0.24 microm. The copolymerized structures lacked any evidence of the sharp nipplelike features observed in the unpolymerized sample, but they did exhibit nanometer-scale detailed surface features, indicative of a higher degree of internal organization. The measured surface roughness of the copolymerized comonomer mixture was more than 10 times greater than the surface roughness of the unpolymerized comonomer mixture.
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PMID:Enzymatic copolymerization alters the structure of unpolymerized mixtures of the biomimetic monomers: the amphiphilic decyl ester of L-tyrosine and L-tyrosineamide--an AFM investigation of nano- to micrometer-scale structure differences. 1536 Mar

We report here on the stereospecificity observed in the action of horseradish peroxidase (HRPC) on monophenol and diphenol substrates. Several enantiomers of monophenols and o-diphenols were assayed: L-tyrosinol, D-tyrosinol, L-tyrosine, DL-tyrosine, D-tyrosine, L-dopa, DL-dopa, D-dopa, L-alpha-methyldopa, DL-alpha-methyldopa, DL-adrenaline, D-adrenaline, L-isoproterenol, DL-isoproterenol and D-isoproterenol. The electronic density at the carbon atoms in the C-1 and C-2 positions of the benzene ring were determined by NMR assays (delta1 and delta2). This value is related to the nucleophilic power of the oxygen atom of the hydroxyl groups and to its oxidation-reduction capacity. The spatial orientation of the ring substituents resulted in lower Km values for L- than for D-isomers. The kcat values for substrates capable of saturating the enzyme were lower for D- than for L-isomers, although both have the same delta1 and delta2 NMR values for carbons C-1 and C-2, and therefore the same oxidation-reduction potential. In the case of substrates that cannot saturate the enzyme, the values of the binding constant for compound II (an intermediate in the catalytic cycle) followed the order: L-isomer>DL-isomer>D-isomer. Therefore, horseradish peroxidase showed stereospecificity in its affinity toward its substrates (K m) and in their transformation reaction rates (k cat).
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PMID:Stereospecificity of horseradish peroxidase. 1565 31


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