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1.
Steinmann D Nauser T Beld J Tanner M Günther D Bounds PL Koppenol WH 《Biochemistry》2008,47(36):9602-9607
The rate constant for the reduction of the tyrosyl radical with selenocysteine has been measured to investigate whether selenocysteine is capable of repair of protein radicals. Tyrosyl radicals, both free in solution and in insulin, were generated by means of pulse radiolysis and laser flash photolysis in aqueous solution. The rate constant for the reaction of free N-acetyl-tyrosyl-amine radicals with selenocysteine is (8 +/- 2) x 10 (8) M (-1) s (-1), and that for tyrosyl radicals in insulin is (1.6 +/- 0.4) x 10 (8) M (-1) s (-1). The rate constant for the reaction of selenoglutathione with the N-acetyl-tyrosyl-amine radical is (5 +/- 2) x 10 (8) M (-1) s (-1). In contrast, cysteine and glutathione react more slowly than their selenium analogues with the tyrosyl radical: the reactions of N-acetyl-tyrosyl-amine radicals with cysteine and glutathione are 3 and 5 orders of magnitude slower, respectively, than those with selenocysteine and selenoglutathione, while those of tyrosyl radicals in insulin are 3 and 2 orders of magnitude slower, respectively. 相似文献
2.
M Hermann S Kapiotis R Hofbauer C Seelos I Held B Gmeiner 《Free radical biology & medicine》1999,26(9-10):1253-1260
The oxidative modification of low density lipoprotein (LDL) may play a significant role in atherogenesis. Tyrosyl radicals generated by myeloperoxidase (MPO) can act as prooxidants of LDL oxidation. Taking into consideration, that monophenolic compounds are able to form phenoxyl radicals in presence of peroxidases, we have tested salicylate, in its ability to act as a prooxidant in the MPO system. Measurement of conjugated dienes and lipid hydroperoxides were taken as indicators of lipid oxidation. Exposure of LDL preparations to MPO in presence of salicylate revealed that the drug could act as a catalyst of lipid oxidation in LDL. The radical scavenger ascorbic acid as well as heme poisons (cyanide, azide) and catalase were inhibitory. The main metabolite of salicylic acid, gentisic acid, showed inhibitory action in the MPO system. Even when lipid oxidation was maximally stimulated by salicylate the LDL oxidation was efficaciously counteracted in presence of gentisic acid at salicylate/gentisic acid ratios that could be reached in plasma of patients receiving aspirin medication. Gentisic acid was also able to impair the tyrosyl radical catalyzed LDL peroxidation. The results suggest that salicylate could act like tyrosine via a phenoxyl radical as a catalyst of LDL oxidative modification by MPO. But the prooxidant activity of this radical species is effectively counteracted by the salicylate metabolite gentisic acid. 相似文献
3.
4.
《Free radical research》2013,47(3-6):375-380
Free radicals, including superoxide anions (O2??), hydroxyl radical (HO'), and hypohalite radical (OCl'), as well as oxidants such as hydrogen peroxide (H2O2) and hypochlorous acid (HOCl), have been indicated in the pathogenesis of myocardial ischemic and reperfusion injury. In this report, we compared the integrity of the myocardial membrane when exposed to these free radicals/oxidants. Isolated rat heart membrane preparations were exposed to chemically generated free radicals with or without their respective scavengers. Membrane fluidity was monitored by fluorescence polarization using the diphenylhexatriene probe, as well as by electron spin resonance (ESR) spectroscopy using 2,2,6,6-tetramethyl piperidine-n-oxyl as the spin labeling agent. HO', H2O2, and OCl' + HOCl increased the fluorescence polarization (FP) and microvis-cosity significantly by 1.7-fold, 1.8-fold, and 1.7-fold, respectively, as compared to an only 1.2– fold increase in FP by O2?? O2?? did not alter the fatty acid profiles of the membrane phospholipids. However, HO' and H2O2 reduced the arachidonic acid contents in phosphatidylcholine (PC), phosphatidylethanolamine (PE), and phosphatidylinositol (PI). These radicals also stimulated the lipid peroxidation by several-fold, while that by O2?? was only insignificant. These results suggest that HO' and H2O2 decreased the membrane fluidity and induced lipid peroxidation by releasing the arachidonic acid from PC, PE. and PI. 相似文献
5.
Through free radical-mediated peroxidation, cyclooxygenase (COX) can metabolize dihomo-γ-linolenic acid (DGLA) and arachidonic acid (AA) to form well-known bioactive metabolites, namely, the 1-series of prostaglandins (PGs1) and the 2-series of prostaglandins (PGs2), respectively. Unlike PGs2, which are generally viewed as proinflammatory and procarcinogenic PGs, PGs1 may possess anti-inflammatory and anti-cancer activity. Previous studies using ovine COX along with spin trapping and the LC/ESR/MS technique have shown that certain exclusive free radicals are generated from different free radical reactions in DGLA and AA peroxidation. However, it has been unclear whether the differences were associated with the contrasting bioactivity of DGLA vs AA. The aim of this study was to refine the LC/MS and spin trapping technique to make it possible for the association between free radicals and cancer cell growth to be directly tested. Using a colon cancer cell line, HCA-7 colony 29, and LC/MS along with a solid-phase extraction, we were able to characterize the reduced forms of radical adducts (hydroxylamines) as the free radicals generated from cellular COX-catalyzed peroxidation. For the first time, free radicals formed in the COX-catalyzed peroxidation of AA vs DGLA and their association with cancer cell growth were assessed (cell proliferation via MTS and cell cycle distribution via propidium iodide staining) in the same experimental setting. The exclusive free radicals formed from the COX-catalyzed peroxidation of AA and DGLA were shown to be correlated with the cell growth response. Our results indicate that free radicals generated from the distinct radical reactions in COX-catalyzed peroxidation may represent the novel metabolites of AA and DGLA that correspond to their contrasting bioactivity. 相似文献
6.
P��ter Nagy Anthony J. Kettle Christine C. Winterbourn 《The Journal of biological chemistry》2009,284(22):14723-14733
The chemistry underlying superoxide toxicity is not fully understood. A
potential mechanism for superoxide-mediated injury involves addition to
tyrosyl radicals, to give peptide or protein hydroperoxides. The rate constant
for the reaction of tyrosyl radicals with superoxide is higher than for
dimerization, but the efficiency of superoxide addition to peptides depends on
the position of the Tyr residue. We have examined the requirements for
superoxide addition and structurally characterized the products for a range of
tyrosyl peptides exposed to a
peroxidase/
system. These included enkephalins as examples of the numerous proteins and
physiological peptides with N-terminal tyrosines. The importance of amino
groups in promoting hydroperoxide formation and effect of methionine residues
on the reaction were investigated. When tyrosine was N-terminal, the major
products were hydroperoxides that had undergone cyclization through conjugate
addition of the terminal amine. With non-N-terminal tyrosine, electron
transfer from
to the peptide radical prevailed. Peptides containing methionine revealed a
novel and efficient intramolecular oxygen transfer mechanism from an initial
tyrosine hydroperoxide to give a dioxygenated derivative with one oxygen on
the tyrosine and the other forming methionine sulfoxide. Exogenous amines
promoted hydroperoxide formation on tyrosyl peptides lacking a terminal amine,
without forming an adduct. These findings, plus the high hydroperoxide yields
with N-terminal tyrosine, can be explained by a mechanism in which hydrogen
bonding of
to the amine increases is oxidizing potential and alters its reactivity. If
this amine effect occurred more generally, it could increase the biological
reactivity of
and have major implications.Free radical-mediated oxidative damage occurs in numerous diseases and is
thought to contribute to the aging process. The primary radical generated by
the reduction of oxygen is superoxide
(),
a relatively benign radical that nevertheless must be removed by superoxide
dismutases (SODs)2 for
an organism to survive in an aerobic environment
(1). A number of potentially
damaging reactions of
have been identified
(1–4).
One of these, which has received relatively little attention, is the addition
of
to other radicals to form hydroperoxides
(5,
6). This reaction has been
shown to occur readily with tyrosine and Tyr-containing dipeptides, resulting
in the formation of tyrosine hydroperoxides
(5–7).
Hydroperoxides are potentially damaging reactive oxygen species. Formation on
proteins can result in detrimental structural and functional changes
(8). Protein hydroperoxides are
also oxidants that can injure other biomolecules.Tyrosyl radicals are generated in many physiological situations and
proteins are major targets for reactive oxidants
(9). In proteins exposed to
free radicals, regardless of the initial site of attack, the resultant radical
commonly localizes to Tyr
(10–13).
Tyrosyl radicals are also produced from tyrosyl peptides through the action of
peroxidases such as myeloperoxidase, and are generated during the catalytic
cycle of enzymes such as ribonucleotide reductase and cyclooxygenase
(14). Tyrosyl radicals undergo
a variety of subsequent reactions. They readily dimerize to form dityrosine,
which has been well documented as a product of oxidative injury
(15,
16). Another oxidative
biomarker, nitrotyrosine, is also formed via tyrosyl radicals
(4,
15,
17). However, one of their
most favored reactions is with
(5,
7,
18,
19). The reaction has a rate
constant several times higher than that for dimerization
(7,
20) and is favored over
dityrosine formation in situations where both tyrosyl and
radicals are generated (7,
20).The reaction of
with phenoxyl radicals results in either repair of the parent phenol (reaction
2, Fig. 1b) or
addition to form a hydroperoxide (reaction 3). With tyrosine, most of the
reacts by addition (7,
20). The structure of tyrosine
hydroperoxide has not been determined directly but inferred from NMR studies
of the corresponding monoxide derivative formed by slow decomposition
(7). These were shown to be
bicyclic compounds formed by conjugate addition of the amino group to the
phenol ring (HOHICA, designated I and named in full in
Fig. 1b, proposed to
arise from reactions 5 and 6).Open in a separate windowFIGURE 1.a, experimental system used for the generation of superoxide and
tyrosyl (TyrO·) radicals. b, proposed mechanism for
the formation and decomposition of tyrosine hydroperoxide derivatives.
R and R′ represent OH and H, respectively, for Tyr, or
amino acid residue(s) for the peptides. Reaction 1 shows
peroxidase-mediated formation of Tyr radicals, which can either dimerize (not
shown) or react with
by electron transfer (reaction 2) or addition (reaction 3).
Addition results in the formation of hydroperoxides (o- and
p-isomers, only the o-isomer shown) that may exist
transiently and decompose to release 1O2 (reaction 4) or
form a stable species that can undergo conjugate addition of the terminal
amino group are shown (when R′= H, reaction 5). An equivalent
reaction is proposed for non-N-terminal Tyr (R′= amino acid residue) in
which conjugation involves the amide nitrogen. Hydrolysis of the
hydroperoxides that are modified by conjugate addition gives the corresponding
hydroxide derivatives (I,
3a-hydroxy-6-oxo-2,3,3a,6,7,7a-hexahydro-1H-indol-2-carboxylic acid or HOHICA)
in reaction 6. c, possible alternative hydrolysis products
(mono-oxygenated derivatives). II, 3,4-dihydroxyphenylalanine
derivatives from the o-isomer; III,
4-alanyl-4-hydroxy-cyclohexadienone (HACHD) derivatives from the
p-isomer.Hydroperoxide formation has been observed with peptides but only when
tyrosine is N-terminal or the reaction is promoted by amino compounds
(5). The amine effect has
implications for hydroperoxide formation on proteins, but the mechanism is not
understood. It has also been postulated that the repair mechanism involves
singlet oxygen release from an intermediate (reaction 4) rather than
electron transfer (reaction 2)
(18), but this has not been
studied experimentally.The objectives of this investigation were to determine the structures of
the hydroperoxide and any other superoxide addition products, and to
understand the mechanism of formation, using a range of synthetic and
physiological tyrosyl peptides. These include the opioids Leu- and
Met-Enkephalin (Leu-Enk, YGGFL; and Met-Enk, YGGFM, respectively) and
Endomorphin 2 (Endo2, YPFF). The opioids have a free N-terminal Tyr that is
essential for activity and are potential physiological targets for
inactivation by
addition. We also investigated whether the presence of a Met residue (as in
Met-Enk) influences Tyr-hydroperoxide formation on the peptide and whether
addition results in the formation of methionine sulfoxide. If so, this could
be a physiological mechanism for production of methionine sulfoxide, which is
one of the most prevalent products of oxidative stress
(21,
22).Peptides were exposed to a xanthine oxidase (XO) system to generate
and hydrogen peroxide (H2O2) plus horseradish peroxidase
(HRP) to catalyze the reaction of H2O2 with the peptide
to give the tyrosyl radical (Fig.
1a). Products were analyzed using a general hydroperoxide
assay (Fe2+/xylenol orange or FOX assay) and by liquid
chromatography/electrospray mass spectrometry (LC/MS). We have obtained
structural information on the hydroperoxides, identified a mechanism of rapid
intramolecular oxidation of Met residues via a hydroperoxide intermediate, and
provide an explanation for why amino groups facilitate the addition of
to the tyrosyl radical. 相似文献
7.
Kapralov AA Yanamala N Tyurina YY Castro L Samhan-Arias A Vladimirov YA Maeda A Weitz AA Peterson J Mylnikov D Demicheli V Tortora V Klein-Seetharaman J Radi R Kagan VE 《Biochimica et biophysica acta》2011,1808(9):2147-2155
Formation of cytochrome c (cyt c)/cardiolipin (CL) peroxidase complex selective toward peroxidation of polyunsaturated CLs is a pre-requisite for mitochondrial membrane permeabilization. Tyrosine residues - via the generation of tyrosyl radicals (Tyr) - are likely reactive intermediates of the peroxidase cycle leading to CL peroxidation. We used mutants of horse heart cyt c in which each of the four Tyr residues was substituted for Phe and assessed their contribution to the peroxidase catalysis. Tyr67Phe mutation was associated with a partial loss of the oxygenase function of the cyt c/CL complex and the lowest concentration of H(2)O(2)-induced Tyr radicals in electron paramagnetic resonance (EPR) spectra. Our MS experiments directly demonstrated decreased production of CL-hydroperoxides (CL-OOH) by Tyr67Phe mutant. Similarly, oxidation of a phenolic substrate, Amplex Red, was affected to a greater extent in Tyr67Phe than in three other mutants. Tyr67Phe mutant exerted high resistance to H(2)O(2)-induced oligomerization. Measurements of Tyr fluorescence, hetero-nuclear magnetic resonance (NMR) and computer simulations position Tyr67 in close proximity to the porphyrin ring heme iron and one of the two axial heme-iron ligand residues, Met80. Thus, the highly conserved Tyr67 is a likely electron-donor (radical acceptor) in the oxygenase half-reaction of the cyt c/CL peroxidase complex. 相似文献
8.
Monica Rossetto Paola Vanzani Michele Lunelli Marina Scarpa Fulvio Mattivi 《Free radical research》2013,47(7):854-859
The inhibition by anthocyanins of the free radical-mediated peroxidation of linoleic acid in a SDS micelle system was studied at pH 7.4 and at 37°C, by oxygraphic and ESR tecniques. The number of peroxyl radicals trapped by anthocyanins and the efficiency of these molecules in the trapping reaction, which are two fundamental aspects of the antioxidant action, were measured and discussed in the light of the molecular structure. In particular the contribution of the substituents to the efficiency is –OH>–OCH3>–H. By ESR we found that the free radicals of anthocyanins are generated in the inhibition of the peroxidation of linoleic acid. The life time of these radical intermediates, the concentration of which ranges from 7 to 59 nM under our experimental conditions, is strictly correlated with the anthocyanin efficiency and with the heat of formation of the radical, as calculated by a semiempirical molecular orbital approach. 相似文献
9.
《Free radical research》2013,47(5):403-418
The peroxidation of liposomes by a haem peroxidase and hydrogen peroxide in the presence of indole-3-acetic acid and derivatives was investigated. It was found that these compounds can accelerate the lipid peroxidation up to 65 fold and this is attributed to the formation of peroxyl radicals that may react with the lipids, possibly by hydrogen abstraction. The peroxyl radicals are formed by peroxidase-catalyzed oxidation of the enhancers to radical cations which undergo cleavage of the carbon-carbon bond on the side-chain to yield CO2 and carbon-centred radicals that rapidly add oxygen. In competition with decarboxylation, the radical cations deprotonate reversibly from the Nl position. Rates of decarboxylation,pKa values and rate of reaction with the peroxidase compound I indicate consistent substituent effects which, however, can not be quantitatively related to the usual Hammett or Brown parameters. Assuming that the rate of decarboxylation of the radical cations taken is a measure of the electron density of the molecule (or radical), it is found that the efficiency of these compounds as enhancers of lipid peroxidation increases with increasing electron density, suggesting that, at least in the model system, the oxidation of the substrates is the limiting step in causing lipid peroxidation. 相似文献
10.
The increasing prevalence of sepsis from Gram-positive bacterial pathogens necessitates further evaluation of the basic assumptions about the molecular pathogenesis of septic shock. Since diverse physiological functions of Gram-positive bacteria are controlled by the degree of esterification of teichoic acids with D-alanine, we examined the reactivity of monosaccharide esters in which anomerically free or protected D-glucose is linked through its C-6 hydroxy group to either phenylalanyl or tyrosyl residues as models for teichoic acid fragment. We show that the attached sugar moiety induces activation of the amino acid residue. Due to the enhanced reactivity of the NH2 group in the monosaccharide esters studied, the formation of products generated by intramolecular and intermolecular glycation reactions is accelerated resulting in heterogeneous mixture of compounds. These findings suggest that, if similar adducts are formed by glycation of D-alanine in teichoic acid of Gram-positive bacteria, they should be examined as potential bioactive ligands or chemical message for infection. 相似文献
11.
van Dalen CJ Winterbourn CC Senthilmohan R Kettle AJ 《The Journal of biological chemistry》2000,275(16):11638-11644
Myeloperoxidase is a heme enzyme of neutrophils that uses hydrogen peroxide to oxidize chloride to hypochlorous acid. Recently, it has been shown to catalyze nitration of tyrosine. In this study we have investigated the mechanism by which it oxidizes nitrite and promotes nitration of tyrosyl residues. Nitrite was found to be a poor substrate for myeloperoxidase but an excellent inhibitor of its chlorination activity. Nitrite slowed chlorination by univalently reducing the enzyme to an inactive form and as a consequence was oxidized to nitrogen dioxide. In the presence of physiological concentrations of nitrite and chloride, myeloperoxidase catalyzed little nitration of tyrosyl residues in a heptapeptide. However, the efficiency of nitration was enhanced at least 4-fold by free tyrosine. Our data are consistent with a mechanism in which myeloperoxidase oxidizes free tyrosine to tyrosyl radicals that exchange with tyrosyl residues in peptides. These peptide radicals then couple with nitrogen dioxide to form 3-nitrotyrosyl residues. With neutrophils, myeloperoxidase-dependent nitration required a high concentration of nitrite (1 mM), was doubled by tyrosine, and increased 4-fold by superoxide dismutase. Superoxide is likely to inhibit nitration by reacting with nitrogen dioxide and/or tyrosyl radicals. We propose that at sites of inflammation myeloperoxidase will nitrate proteins, even though nitrite is a poor substrate, because the co-substrate tyrosine will be available to facilitate the reaction. Also, production of 3-nitrotyrosine will be most favorable when the concentration of superoxide is low. 相似文献
12.
K. A. Balasubramanian S. Nalini M. Manohar 《Molecular and cellular biochemistry》1992,111(1-2):131-135
Oxygen free radicals damage cells through peroxidation of membrane lipids. Gastrointestinal mucosal membranes were found to be resistant to in vitro lipid peroxidation as judged by malonaldehyde and conjugated diene production and arachidonic acid depletion. The factor responsible for this in this membrane was isolated and chemically characterised as the nonesterified fatty acids (NEFA), specifically monounsaturated fatty acid, oleic acid. Authentic fatty acids when tested in vitro using liver microsomes showed similar inhibition. The possible mechanism by which NEFA inhibit peroxidation is through iron chelation and iron-fatty acid complex is incapable of inducing peroxidation. Free radicals generated independent of iron was found to induce peroxidaton of mucosal membranes. Gastrointestinal mucosal membranes were found to contain unusually large amount of NEFA. Circulating albumin is known to contain NEFA which was found to inhibit iron induced peroxidation whereas fatty acid free albumin did not have any effect. Addition of individual fatty acids to this albumin restored its inhibitory capacity among which monounsaturated fatty acids were more effective. These studies have shown that iron induced lipid peroxidation damage is prevented by the presence of nonesterified fatty acids. 相似文献
13.
Tyrosyl radicals cross-linked to protein tyrosine residues (tyrosylated proteins) represent hallmarks of neutrophil-mediated injury at the inflammatory locus. Yet the proteins targeted by tyrosyl radicals in an intact cellular system remain to be elucidated. Here, we show that tyrosyl radicals generated by human neutrophils after activation by phorbol 12-myristate 13-acetate (PMA), interferon-gamma (IFN-gamma) or TNF-alpha could act in an autocrine manner by cross-linking to endogenous proteins. We have identified the tyrosylated proteins by using a membrane-impermeable tyrosine analogue, tyramine coupled to fluorescein (TyrFluo), in combination with proteomics techniques. Confocal microscopy images indicated that initially the tyrosylated proteins were localized in patches at the cell surface to become internalized subsequently. In the neutrophil membrane-associated proteome, lactoferrin was the prime target of tyrosylation. Out of three isoforms identified, an 80 kDa neutral isoform was tyrosylated more extensively than the 85 kD basic isoform, particularly after PMA activation. Although all three stimuli induced tyrosylation of the filamentous component vimentin, additional tyrosylated vimentin fragments were detected after IFN-gamma- and TNF-alpha-stimulation. Moreover, upon activation the bulk of vimentin behaved as a dimer (M(r) 120 kDa) being slightly tyrosylated, yet phosphorylated at Thr-425 possibly as a requirement for its externalization. Unexpectedly, bovine catalase added to end tyrosyl radicals formation was detected as a highly tyrosylated neutrophil-associated protein. A moderate stimulus-dependent tyrosylation of ATP synthase-beta, alpha-enolase, glyceraldehyde 3-phosphate dehydrogenase, cytokeratin-10, filamin-A, and annexin-I was also observed. When the membrane-permeable probe (acetylTyrFluo) was used, protein tyrosylation was not observed indicating that the intracellular proteins were well protected against oxidative attack. This study shows that human neutrophils can modulate their proteome via a tyrosine oxidation pathway induced by pro-inflammatory mediators. 相似文献
14.
Mouse and human spermatozoa, but not rabbit spermatozoa, have long been known to be sensitive to loss of motility induced by exogenous H2O2. Recent work has shown that loss of sperm motility in these species correlates with the extent of spontaneous lipid peroxidation. In this study, the effect of H2O2 on this reaction in sperm of the three species was investi gated. The rate of spontaneous lipid peroxidation in mouse and human sperm is markedly enhanced in the presence of 1-5 mM H2O2, while the rate in rabbit sperm is unaffected by H2O2. The enhancement of lipid peroxidation, the rate of reaction of H2O2 with the cells, the activity of sperm glutathione peroxidase, and the endogenous glutathione content are highest in mouse sperm, intermediate in human sperm, and very low in rabbit sperm. Inac tivation of glutathione peroxidase occurs in the presence of H2O2 due to complete conver sion of endogenous glutathione to GSSG: No GSH is available as electron donor substrate to the peroxidase. Inactivation of glutathione peroxidase by the inhibitor mercaptosucci nate has the same effect on rate of lipid peroxidation and loss of motility in mouse and human sperm as does H2O2. This implies that H2O2 by itself at 1-5 mM is not intrinsically toxic to the cells. With merceptosuccinate, the endogenous glutathione is present as GSH in mouse and human sperm, indicating that the redox state of intracellular glutathione by itself plays little role in protecting the cell against spontaneous lipid peroxidation. Mouse and human sperm also have high rates of superoxide production. We conclude that the key intermediate in spontaneous lipid peroxidation is lipid hydroperoxide generated by a chain reaction initiated by and utilizing superoxide. Removal of this hydroperoxide by gluta thione peroxidase protects these sperm against peroxidation; inactivation of the peroxidase allows lipid hydroperoxide to increase and so increases the peroxidation rate. Rabbit sperm have low rates of superoxide reaction due to high activity of their superoxide dismutase; lack of endogenous glutathione and low peroxidase activity does not affect their rate or lipid peroxidation. As a result, these sperm are not affected by either H2O2 or mercapto-succinate. These results lead us to postulate a mechanism for spontaneous lipid peroxida tion in mammalian sperm which involves reaction of lipid hydroperoxide and O2 as the rate-determining step. 相似文献
15.
Fausta Natella Mirella Nardini Fulvio Ursini Cristina Scaccini 《Free radical research》2013,47(5):427-434
Heme-peroxidases, such as horseradish peroxidase (HRP), are among the most popular catalysts of low density lipoprotein (LDL) peroxidation. In this model system, a suitable oxidant such as H2O2 is required to generate the hypervalent iron species able to initiate the peroxidative chain. However, we observed that traces of hydroperoxides present in a fresh solution of linoleic acid can promote lipid peroxidation and apo B oxidation, substituting H2O2.Spectral analysis of HRP showed that an hypervalent iron is generated in the presence of H2O2 and peroxidizing linoleic acid. Accordingly, careful reduction of the traces of linoleic acid lipid hydroperoxide prevented formation of the ferryl species in HRP and lipid peroxidation. However, when LDL was oxidized in the presence of HRP, the ferryl form of HRP was not detectable, suggesting a Fenton-like reaction as an alternative mechanism. This was supported by the observation that carbon monoxide, a ligand for the ferrous HRP, completely inhibited peroxidation of LDL.These results are in agreement with previous studies showing that myoglobin ferryl species is not produced in the presence of phospholipid hydroperoxides, and emphasize the relevance of a Fenton-like chemistry in peroxidation of LDL and indirectly, the role of pre-existing lipid hydroperoxides. 相似文献
16.
Rania Dumarieh Jennifer D'Antonio Alexandria Deliz-Liang Tatyana Smirnova Dimitri A. Svistunenko Reza A. Ghiladi 《The Journal of biological chemistry》2013,288(46):33470-33482
Dehaloperoxidase (DHP) from Amphitrite ornata, having been shown to catalyze the hydrogen peroxide-dependent oxidation of trihalophenols to dihaloquinones, is the first oxygen binding globin that possesses a biologically relevant peroxidase activity. The catalytically competent species in DHP appears to be Compound ES, a reactive intermediate that contains both a ferryl heme and a tyrosyl radical. By simulating the EPR spectra of DHP activated by H2O2, Thompson et al. (Thompson, M. K., Franzen, S., Ghiladi, R. A., Reeder, B. J., and Svistunenko, D. A. (2010) J. Am. Chem. Soc. 132, 17501–17510) proposed that two different radicals, depending on the pH, are formed, one located on either Tyr-34 or Tyr-28 and the other on Tyr-38. To provide additional support for these simulation-based assignments and to deduce the role(s) that tyrosyl radicals play in DHP, stopped-flow UV-visible and rapid-freeze-quench EPR spectroscopic methods were employed to study radical formation in DHP when three tyrosine residues, Tyr-28, Tyr-34, and Tyr-38, were replaced either individually or in combination with phenylalanines. The results indicate that radicals form on all three tyrosines in DHP. Evidence for the formation of DHP Compound I in several tyrosine mutants was obtained. Variants that formed Compound I showed an increase in the catalytic rate for substrate oxidation but also an increase in heme bleaching, suggesting that the tyrosines are necessary for protecting the enzyme from oxidizing itself. This protective role of tyrosines is likely an evolutionary adaptation allowing DHP to avoid self-inflicted damage in the oxidative environment. 相似文献
17.
γ-Linolenic acid (GLA) has been reported as a potential anti-cancer and anti-inflammatory agent and has received substantial attention in cancer care research. One of the many proposed mechanisms for GLA biological activity is free radical-mediated lipid peroxidation. However, no direct evidence has been obtained for the formation of GLA-derived radicals. In this study, a combination of LC/ESR and LC/MS was used with α-[4-pyridyl-1-oxide]-N-tert-butyl nitrone (POBN) to profile the carbon-centred radicals that are generated in lipoxygenase-catalysed GLA peroxidation. A total of four classes of GLA-derived radicals were characterized including GLA-alkyl, epoxyallylic, dihydroxyallylic radicals and a variety of carbon-centred radicals stemming from the β-scissions of GLA-alkoxyl radicals. By means of an internal standard in LC/MS, one also quantified each radical adduct in all its redox forms, including an ESR-active form and two ESR-silent forms. The results provided a good starting point for ongoing research in defining the possible biological effects of radicals generated from GLA peroxidation. 相似文献
18.
The transition metal elements like copper act as double-edged sword for living cells. Cu, a redox active metal, is essential for various biological processes, but at higher concentrations it leads to toxicity by inducing production of reactive oxygen species (ROS). Thus, the objective of the present study was to investigate the effects of exogenously applied castasterone on oxidative stress markers and redox homeostasis managers in Brassica juncea plants subject to copper stress for 30 days. Copper-exposed plants showed accumulation of free radicals (H2O2 and superoxide anion) and lipid peroxidation. However, the exogenous treatment of seeds via the seed soaking method with different concentrations of castasterone reduced H2O2 production, superoxide anion radical content, and lipid peroxidation, thus indicating improved detoxification of ROS. Enzyme activity was increased by 19.19% for guaiacol peroxidase, 16.20% for superoxide dismutase, 35.74% for glutathione peroxidase, 27.58% for dehydroascorbate reductase, and 42.75% for ascorbate peroxidase, with castasterone pre-soaking under copper stress. The levels of non-enzymatic antioxidants were also increased with castasterone pre-treatment under copper stress. It may be concluded that castasterone treatment enhanced redox homeostasis managers in addition to increased levels of osmoprotectants. 相似文献
19.
Janusz M. Gebicki Thomas Nauser Anastasia Domazou Daniel Steinmann Patricia L. Bounds Willem H. Koppenol 《Amino acids》2010,39(5):1131-1137
The oxidation of proteins and other macromolecules by radical species under conditions of oxidative stress can be modulated
by antioxidant compounds. Decreased levels of the antioxidants glutathione and ascorbate have been documented in oxidative
stress-related diseases. A radical generated on the surface of a protein can: (1) be immediately and fully repaired by direct
reaction with an antioxidant; (2) react with dioxygen to form the corresponding peroxyl radical; or (3) undergo intramolecular
long range electron transfer to relocate the free electron to another amino acid residue. In pulse radiolysis studies, in
vitro production of the initial radical on a protein is conveniently made at a tryptophan residue, and electron transfer often
leads ultimately to residence of the unpaired electron on a tyrosine residue. We review here the kinetics data for reactions
of the antioxidants glutathione, selenocysteine, and ascorbate with tryptophanyl and tyrosyl radicals as free amino acids
in model compounds and proteins. Glutathione repairs a tryptophanyl radical in lysozyme with a rate constant of (1.05 ± 0.05) × 105 M–1 s–1, while ascorbate repairs tryptophanyl and tyrosyl radicals ca. 3 orders of magnitude faster. The in vitro reaction of glutathione
with these radicals is too slow to prevent formation of peroxyl radicals, which become reduced by glutathione to hydroperoxides;
the resulting glutathione thiyl radical is capable of further radical generation by hydrogen abstraction. Although physiologically
not significant, selenoglutathione reduces tyrosyl radicals as fast as ascorbate. The reaction of protein radicals formed
on insulin, β-lactoglobulin, pepsin, chymotrypsin and bovine serum albumin with ascorbate is relatively rapid, competes with
the reaction with dioxygen, and the relatively innocuous ascorbyl radical is formed. On the basis of these kinetics data,
we suggest that reductive repair of protein radicals may contribute to the well-documented depletion of ascorbate in living
organisms subjected to oxidative stress. 相似文献
20.
Hao Zhang 《Archives of biochemistry and biophysics》2009,484(2):134-618
Recent reports suggest that intramolecular electron transfer reactions can profoundly affect the site and specificity of tyrosyl nitration and oxidation in peptides and proteins. Here we investigated the effects of methionine on tyrosyl nitration and oxidation induced by myeloperoxidase (MPO), H2O2 and NO2− and peroxynitrite (ONOO−) or ONOO− and bicarbonate (HCO3−) in model peptides, tyrosylmethionine (YM), tyrosylphenylalanine (YF) and tyrosine. Nitration and oxidation products of these peptides were analyzed by HPLC with UV/Vis and fluorescence detection, and mass spectrometry; radical intermediates were identified by electron paramagnetic resonance (EPR)-spin-trapping. We have previously shown (Zhang et al., J. Biol. Chem. 280 (2005) 40684-40698) that oxidation and nitration of tyrosyl residue was inhibited in tyrosylcysteine(YC)-type peptides as compared to free tyrosine. Here we show that methionine, another sulfur-containing amino acid, does not inhibit nitration and oxidation of a neighboring tyrosine residue in the presence of ONOO− (or ONOOCO2−) or MPO/H2O2/NO2− system. Nitration of tyrosyl residue in YM was actually stimulated under the conditions of in situ generation of ONOO− (formed by reaction of superoxide with nitric oxide during SIN-1 decomposition), as compared to YF, YC and tyrosine. The dramatic variations in tyrosyl nitration profiles caused by methionine and cysteine residues have been attributed to differences in the direction of intramolecular electron transfer in these peptides. Further support for the interpretation was obtained by steady-state radiolysis and photolysis experiments. Potential implications of the intramolecular electron transfer mechanism in mediating selective nitration of protein tyrosyl groups are discussed. 相似文献