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)

Oxidatively modified LDLs are antigenic and elicit the generation of autoantibodies often detected in plasma and within plaques of atherosclerotic patients. Although Cu(2+)-oxidized LDL and malondialdehyde (MDA)-modified LDL are usually used as antigens in immunoassays, other, still unrecognized epitopes may be formed in vivo during LDL oxidation and may induce antibody production. Antibodies recognizing LDL oxidatively modified by Cu2+, 2,2'-azobis-(2-amidino propane) hydrochloride (AAPH), and the combination of horseradish peroxidase and H2O2 (HRP) were detected in serum of a group of 90 unselected patients. HRP-oxidized LDL was the antigen that revealed the highest IgG titers, although the extent of LDL oxidation (evaluated as conjugated diene formation, loss of tryptophan fluorescence, production of fluorescent aldehydic adducts, and change in electrophoretic mobility) was comparable to that obtained with Cu2+ and AAPH. There was a highly statistically significant correlation between the IgG titers detected using Cu(2+)- and AAPH-oxidized LDLs as antigens, but no correlation was found between the IgG titers revealed by HRP and Cu2+ or AAPH. In addition, the antibody titers against MDA-modified LDL exhibited a significant correlation with those against Cu(2+)- or AAPH-oxidized LDL but did not correlate with those against HRP-oxidized LDL. Finally, immunocompetition experiments revealed that IgG recognizing HRP-oxidized LDL did not cross-react with Cu(2+)-oxidized LDL and vice versa. The possibility that lipid peroxidation-independent modifications could play a role in HRP-induced formation of antigenic epitopes in LDL was supported by two lines of evidence. First, in probucol-enriched LDL, despite the complete inhibition of lipid peroxidation, HRP, but not Cu2+ and AAPH, was still able to generate epitopes that were recognized by the same sera reacting with HRP-oxidized native (not probucol-enriched) LDL. In addition, the presence of autoantibodies against Cu(2+)- and AAPH-oxidized LDLs was negatively correlated with serum alpha-tocopherol concentration, whereas the titers against HRP-oxidized LDL did not exhibit any statistically relevant correlation with alpha-tocopherol levels. Together, these findings indicate that peroxidase(s)-dependent mechanisms can trigger peculiar lipid peroxidation-independent modifications of LDL in vivo.
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PMID:Circulating autoantibodies recognizing peroxidase-oxidized low density lipoprotein. Evidence for new antigenic epitopes formed in vivo independently from lipid peroxidation. 901 48

NO and NO-donors are able to inhibit the peroxidation of polyunsaturated fatty acids in human low-density lipoproteins (LDL) exposed to Cu+2. Here we report that 1-hydroxy-2-oxo-3,3-bis(3-aminoethyl)-1-triazene (NOC-18), a compound which releases NO at low rate in aqueous solutions, powerfully inhibits the peroxidation of polyunsaturated fatty acids, tryptophan loss, the formation of fluorescent aldehydic adducts in apo B100 and the increase of electrophoretic mobility in isolated LDL undergoing oxidation. The inhibitory effect is not restricted to Cu+2-induced peroxidation but is also detectable with other oxidizing conditions such as the free radical generator 2,2'-azobis-(2-amidino propane) hydrochloride (AAPH), the combination of horseradish peroxidase and H2O2 (HRP), and peroxynitrite (ONOO-). The recognition of Cu+2-, AAPH-, and ONOO(-)-modified LDL by specific autoantibodies present in serum of atherosclerotic patients is almost completely inhibited when the oxidation procedure is performed in the presence of NOC-18. However, NOC-18 is completely ineffective in preventing the formation of recognizable antigens in HRP-modified LDL. These findings suggest that NO may efficiently prevent the formation of some, but not all, the antigenic epitopes recognized by human autoantibodies and thus likely formed during in vivo LDL oxidation.
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PMID:The formation of some antigenic epitopes in oxidized human low-density lipoprotein is inhibited by nitric oxide. 912 22

Lignin peroxidases (LiP) from the white-rot fungus Phanerochaete chrysosporium oxidize veratryl alcohol (VA) by two electrons to veratryl aldehyde, although the VA cation radical (VA.+) is an intermediate [Khindaria, A., et al. (1995) Biochemistry 34, 6020-6025]. It was speculated, on the basis of kinetic evidence, that VA*+ can form a catalytic complex with LiP compound II. We have used low-temperature EPR to provide direct evidence for the formation of the complex. The EPR spectrum of VA*+ obtained at 4 K was explained by a model for coupling between the oxoferryl moiety of the heme (S = 1) and VA.+ (S = 1/2) similar to the model proposed for an oxyferryl and a porphyrin pi cation radical of horseradish peroxidase. The coupling constant suggested that VA.+ was equally ferro- and antiferromagnetically coupled to the oxoferryl moiety. The spectrum was simulated with g perpendicular only marginally greater than g parallel. This was surprising since the only other known organic radical coupled to the heme iron in a peroxidase is the tryptophan cation radical in cytochrome c peroxidase which exhibits a g tensor with g parallel greater than g perpendicular. Spin concentration analysis suggested that the 1 mol of VA*+ was coupled to the oxoferryl moiety per mole of enzyme. The VA.+ signal decayed with a first-order decay constant of 1.76 s-1, in close agreement with the earlier published decay constant of 1.85 s-1 from room-temperature EPR studies. The exchange coupling between VA.+ and the oxoferryl moiety strongly advocates calling this species (VA.+ and LiP compound II) a catalytic complex.
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PMID:Detection and characterization of the lignin peroxidase compound II-veratryl alcohol cation radical complex. 936 91

The oxidation of tryptophan and indole-3-acetic acid (IAA) by the dibromine radical anion or peroxidase from horseradish in aqueous solution was investigated and compared, especially with respect to the involvement of oxygen and superoxide. Using EPR with spin-trapping, the tryptophanyl radical, generated by either method was found to react with oxygen, although this reaction is too slow to be observed by pulse radiolysis (k < 5 x 10(6) dm3 mol-1 s-1). No superoxide results from this reaction, thus excluding an electron-transfer mechanism and suggesting the formation of a tryptophan peroxyl radical, possibly in a reversible process. These observations imply that in proteins where the tryptophanyl radical exists as a stable species it must either have its reactivity modified by the protein environment or be inaccessible to oxygen. The related molecule LAA is oxidized by either peroxidase or Br2.- to a radical cation that decarboxylates to yield a skatolyl radical. The latter reacts with oxygen to give a peroxyl radical that does not release superoxide. However, O2.- is formed during the peroxidase-catalyzed oxidation of indoleacetic acid. This supports the hypothesis that the peroxidase can act in an oxidase cycle involving ferrous enzyme and compound III, with superoxide as a product.
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PMID:The reaction of oxygen with radicals from oxidation of tryptophan and indole-3-acetic acid. 939 27

We have shown earlier that restraint-cold stress-induced gastric ulceration in rats is caused by metal ion-dependent generation of hydroxyl radical (OH.) and oxidative inactivation of the gastric peroxidase (GPO), an important H2O2 scavenging enzyme. To study the mechanism of the oxidative damage of GPO, the purified enzyme was exposed to an OH. generating system containing Cu2+, ascorbate, and H2O2. Kinetic studies indicate that the enzyme is inactivated in a time-dependent process showing saturation with respect to Cu2+ concentration. The enzyme specifically requires Cu2+ and is not inactivated by the same concentration of Fe2+, Mn2+, or Zn2+. Sensitivity to catalase indicates the critical role of H2O2 in the inactivation. Inactivation is insensitive to superoxide dismutase, suggesting no role of superoxide. The rate of inactivation is not increased in D2O excluding the involvement of singlet oxygen in the process. However, OH. scavengers such as benzoate or mannitol cannot prevent inactivation. The results indicate a plausible generation of OH. within the enzyme molecule as the cause of inactivation. Fragmentation of peptide linkage or intramolecular crosslinking, gross change of tertiary structure, or change in intrinsic tryptophan fluorescence which occurs in "global" oxidation are not evident. Inactivation is dependent on pH and from a plot of K(obs) of inactivation against pH, the controlling role of an ionizable group of the enzyme having a pka of 7.8 could be suggested, deprotonation of which favors inactivation. Amino acid analysis shows a specific loss of two lysine residues in the inactivated enzyme. Competitive kinetic studies indicate that pyridoxal phosphate, a specific modifier of the lysine residue, prevents inactivation by competing with Cu2+ for binding at the GPO. A Cu2+ binding motif consisting at least of two lysine residues exists in GPO, which specifically binds Cu2+ and generates OH.. The radical oxidizes the lysine residues and perturbs the heme environment to cause inactivation. We suggest that oxidative damage of GPO is mediated by site-specific generation of OH. and not by the OH. generated in the bulk phase.
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PMID:Oxidative inactivation of gastric peroxidase by site-specific generation of hydroxyl radical and its role in stress-induced gastric ulceration. 943 59

There are two known isoforms of prostaglandin H synthase (PGHS), a key enzyme in the conversion of arachidonic acid to bioactive prostanoids. The "constitutive" isoform, PGHS-1, is thought to have housekeeping functions, and the "inducible" isoform, PGHS-2, has been implicated in cellular responses to cytokines. The two isoforms have high sequence conservation in the cyclooxygenase active site and quite similar crystallographic structures, but differ markedly in their interactions with many cyclooxygenase substrates and inhibitors. We have evaluated the stability of the overall folding, and of the active sites of ovine PGHS-1 and human PGHS-2 using denaturation with guanidinium hydrochloride (GdmHCl). Changes in hydrodynamic and cross-linking properties indicated a dimer --> monomer transition for both isoforms between 0.5 and 2 M GdmHCl; the monomers unfolded at higher GdmHCl levels. Changes in overall secondary and tertiary structure, measured by tryptophan fluorescence and circular dichroism, occurred in two phases for each isoform, with the transition between the phases at 0.2-0.5 M GdmHCl. Disruption of active site functions (cyclooxygenase, peroxidase, and cyclooxygenase inhibitor binding activities) began at GdmHCl levels below 0.2 M. The structural and functional changes were completely reversible up to about 2 M GdmHCl, they were more pronounced at lower protein levels, and they required lower GdmHCl levels for PGHS-2 than for PGHS-1. The results are consistent with a four-state denaturation process for both isoforms: native dimers --> inactive dimers --> compact monomers --> unfolded monomers. The first two steps are reversible for both isoforms; PGHS-2 undergoes the first and last steps more readily than PGHS-1. Thus, the structural stability of PGHS-2, both in the active site regions and in the subunits overall, is distinctly less than that of PGHS-1. These differences in structural stability may contribute to the isoforms' active site ligand selectivity.
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PMID:Comparison of structural stabilities of prostaglandin H synthase-1 and -2. 950 82

The crucial reaction intermediate in the reaction of peroxidase with hydrogen peroxide (H2O2), compound I, contains a porphyrin pi-cation radical in horseradish peroxidase (HRP), which catalyzes oxidation of small organic and inorganic compounds, whereas cytochrome c peroxidase (CcP) has a radical center on the tryptophan residue (Trp-191) and oxidizes the redox partner, cytochrome c. To investigate the roles of the amino acid residue near the heme active center in discriminating the function of the peroxidases in these two enzymes, we prepared a CcP-like HRP mutant, F221W (Phe-221 --> Trp). Although the rapid spectral scanning and stopped-flow experiments confirmed that the F221W mutant reacts with H2O2 to form the porphyrin pi-cation radical at the same rate as for the wild-type enzyme, the characteristic spectral features of the porphyrin pi-cation radical disappeared rapidly, and were converted to the compound II-type spectrum. The EPR spectrum of the resultant species produced by reduction of the porphyrin pi-cation radical, however, was quite different from that of compound II in HRP, showing typical signals from a Trp radical as found for CcP. The sequential radical formation from the porphyrin ring to the Trp residue implies that the proximal Trp is a key residue in the process of the radical transfer from the porphyrin ring, which differentiates the function of peroxidases.
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PMID:Detection of a tryptophan radical as an intermediate species in the reaction of horseradish peroxidase mutant (Phe-221 --> Trp) and hydrogen peroxide. 961 74

The aim of this study was to further clarify which part of human low density lipoprotein (LDL) is attacked by the MPO/H2O2/Cl- -system and which reactive oxygen species is responsible for the attack. Therefore the influence of this system on the modification of the lipid and protein moiety of LDL was studied in vitro. Using the monochlorodimedone assay it was found that HOCl is produced in micromolar quantities in the absence of LDL and is rapidly consumed by LDL in a concentration dependent manner. The consumption of HOCl was reflected in the formation of HOCl-specific epitopes on apo B-100 as determined by an antibody raised against HOCl-modified LDL. The absorbency at 234 nm was applied to measure continuously the extent of modification of LDL. The general kinetic pattern of the absorbency measurement consisted of a lag phase where no LDL modification was observed, followed by a rapid increase of absorbency and a plateau phase. Finally the absorbency decreased due to LDL precipitation. Time dependent absorption spectra indicated that this kinetic pattern is mainly caused by light scattering due to particle aggregation rather than by a specific absorption at 234 nm due to conjugated diene formation. In agreement with this finding a low rate of thiobarbituric acid reactive substances (TBArS) formation was observed after a lag phase. The aggregation of LDL occurs most likely by modification of apo B-100, which was determined fluorimetrically in terms of LDL-tryptophan destruction in presence of the MPO/H2O2/Cl(-)-system. The kinetic course of tryptophan fluorescence generally consisted of a rapid decrease leveling off into a low plateau phase. Gas chromatographic determinations of linoleic acid in LDL in presence of the MPO system showed that this polyunsaturated fatty acid (PUFA) is easily attacked by HOCl. Consistent with this finding NMR spectra of HOCl modified LDL indicated a complete disappearance of bis-allylic methylene groups. Since lipid peroxidation products only partially account for this loss of PUFAs, other reactions of HOCl with unsaturated lipids--probably chlorohydrin formation--must be involved. Summarizing, although the rate of lipid peroxidation is low, both the lipid and the protein moiety of LDL are readily modified by the MPO system. It appears that the immediate consequence of apo B-100 modification is its aggregation. It is concluded that MPO, which has been detected in atherosclerotic lesions, is able to contribute to the modification of LDL into a form recognizable for uncontrolled uptake by macrophages.
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PMID:Human low density lipoprotein as a target of hypochlorite generated by myeloperoxidase. 962 68

A monocotyledonous tree, Roystonea regia, was found to bear root nodules. The root nodules contained a high amount (16.9 microg/g fresh mass) of indole acetic acid (IAA). A big tryptophan pool (1555.1 microg/g fresh mass) was found in the root nodules, which might serve as a source of IAA production. The presence of IAA-metabolizing enzymes IAA oxidase and peroxidase indicated metabolism of IAA in the root nodules. The symbiont isolated from the root nodules of R. regia, a Rhizobium sp., produced high amount of IAA in culture when supplemented with tryptophan. The possible role of this IAA production in the monocotyledonous tree-Rhizobium symbiosis is discussed.
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PMID:Indole acetic acid and its metabolism in root nodules of a monocotyledonous tree Roystonea regia. 966 15

The topology of the binding site has been studied for two monoclonal antibodies 13G10 and 14H7, elicited against iron(III)-alpha,alpha,alpha,beta-meso-tetrakis(ortho-carboxyphenyl)porph yrin [alpha,alpha,alpha, beta-Fe[(o-COOHPh)4-porphyrin]], and which exhibit in the presence of this alpha,alpha,alpha, beta-Fe[(o-COOHPh)4-porphyrin] cofactor a peroxidase activity. A comparison of the dissociation constants of the complexes of 13G10 and 14H7 with various tetra-aryl-substituted porphyrin has shown that: (a) the central iron(III) atom of alpha,alpha,alpha,beta-Fe[(o-COOHPh)4-porphyrin] is not recognized by either of the two antibodies; and (b) the ortho-carboxylate substituents of the meso-phenyl rings of alpha,alpha,alpha, beta-Fe[(o-COOHPh)4-porphyrin] are essential for the recognition of the porphyrin by 13G10 and 14H7. Measurement of the dissociation constants for the complexes of 13G10 and 14H7 with the four atropoisomers of (o-COOHPh)4-porphyrinH2 as well as mono- and di-ortho-carboxyphenyl-substituted porphyrins suggests that the three carboxylates in the alpha, alpha, beta position are recognized by both 13G10 and 14H7 with the two in the alpha, beta positions more strongly bound to the antibody protein. Accordingly, the topology of the active site of 13G10 and 14H7 has roughly two-thirds of the alpha,alpha,alpha,beta-Fe[(o-COOHPh)4-porphyrin] cofactor inserted into the binding site of the antibodies, with one of the aryl ring remaining outside. Three of the carboxylates are bound to the protein but no amino acid residue acts as an axial ligand to the iron atom. Chemical modification of lysine, histidine, tryptophan and arginine residues has shown that only modification of arginine residues causes a decrease in both the binding of alpha,alpha,alpha, beta-Fe[(o-COOHPh)4-porphyrin] and the peroxidase activity of both antibodies. Consequently, at least one of the carboxylates of the hapten is bound to an arginine residue and no amino acids such as lysine, histidine or tryptophan participate in the catalysis of the heterolytic cleavage of the O-O bond of H2O2. In addition, the amino acid sequence of both antibodies not only reveals the presence of arginine residues, which could be those involved in the binding of the carboxylates of the hapten, but also the presence of several amino acids in the complementary determining regions which could bind other carboxylates through a network of H bonds.
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PMID:Active site topology of artificial peroxidase-like hemoproteins based on antibodies constructed from a specifically designed ortho-carboxy-substituted tetraarylporphyrin. 979 10


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