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Showing 1641–1660 of 2058 publications.
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Terentis, Andrew C.; Thomas, Shane R.; Burr, Jeanne A.; Liebler, Daniel C.; Stocker, RolandOxidation of low-density lipoproteins (LDL) is a key process in atherogenesis, and vitamin E (?-tocopherol, TOH) has received attention for its potential to attenuate the disease. Despite this, the type and extent of TOH oxidation and its relationship to lipid oxidation in the vessel wall where lesions develop remain unknown. Therefore, we measured oxidized lipids, TOH, and its oxidation products, ?-tocopherylquinone (TQ), 2,3- and 5,6-epoxy-?-tocopherylquinones by gas chromatography-mass spectrometry analysis in human lesions representing different stages of atherosclerosis. We also oxidized LDL in vitro to establish "footprints" of TOH oxidation product for different oxidants. The in vitro studies demonstrated that tocopherylquinone epoxides are the major products when LDL is exposed to the one-electron (ie, radical) oxidants, peroxyl radicals, and copper ions, whereas TQ preferentially accumulates with the two-electron (nonradical) oxidants, hypochlorite, and peroxynitrite. In human lesions, the relative extent of TOH oxidation was maximal early in the disease where it exceeded lipid oxidation. Independent of the disease stage, TQ was always the major oxidation product with all products together representing <20% of the total TOH present, and the oxidation product profile mirroring that formed during LDL oxidation by activated monocytes in the presence of nitrite. In contrast, oxidized lipid increased with increasing disease severity. These results suggest that two-electron oxidants are primarily responsible for TOH oxidation in the artery wall, and that the extent of TOH oxidation is limited yet substantial lipid oxidation takes place. This study may have important implications regarding antioxidant supplements aimed at preventing LDL oxidation and hence atherogenesis.
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Tan, Hiok C.; Fung, Kevin C.; Kritharides, LeonardBackground: Doppler spectrum of tricuspid regurgitation (TR) is used to noninvasively assess right ventricular (RV) pressure. With mild TR, the native (Nat) TR envelope may not allow accurate pressure evaluation. Proprietary contrast agents, such as Levovist (Lev) can be used to augment TR Doppler and opacify right-sided heart chambers, but they are expensive, and their efficacy has not been objectively evaluated in patients with difficult baseline studies or compared with less expensive saline (Sal) or colloid solutions, such as Gelofusine (Gel). Methods: Twenty-five consecutive patients with poor quality Nat TR envelopes on transthoracic echocardiogram were reexamined after serial intravenous injection of 3 contrast agents (Sal, Gel, and Lev). Doppler signals for each agent recorded on video and digitally on optical disk were assessed for signal quality, estimated RV pressure, interobserver and intraobserver variation, and longevity of signal. Quality of right ventricular-right atrial (RV-RA) opacification was also determined for Sal and Gel. Of the 25 patients, 9 underwent percutaneous right-sided heart catheterization. We used the pressures obtained from the catheterization to independently evaluate the pressure estimates from echocardiography. Results: All 3 contrast agents significantly improved the mean quality grade (grades 0-5) of TR envelopes (Nat 1.12, Sal 1.97, Gel 2.56, Lev 2.41, P < .001), decreased the number of uninterpretable envelopes (grade 0) (Nat 49%, Sal 12%, Gel 4%, Lev 12%, P < .0001 for comparison of each agent relative to Nat), and improved the correlation between echocardiographic and catheter-derived RV-RA pressure measurements (Nat r = 0.65, Sal r = 0.75, Gel r = 0.90, Lev r = 0.88). The persistence of enhanced Doppler signals of interpretable quality (> grade 1) was greater for Lev (15.8 seconds) and Gel (15 seconds) than Sal (7.6 seconds) (P = .002). Opacification of RV and RA, measured as mean luminosity score during 2-dimensional harmonic imaging, was significantly higher for Gel than Sal (92.84 31.2 vs 56.06 25-6, respectively; P = .0003). Sal, Gel and Lev, respectively, cost $0.10, $2.50, and $75.00 per study. Conclusion: Agitated colloid is a novel, effective, and inexpensive alternative to proprietary agents and saline for the assessment of pulmonary systolic pressure and right-sided heart opacification. Copyright 2002 by the American Society of Echocardiography.
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Jennings, Garry L.R.; Dilley, Rodney James[No abstract available]
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Kritharides, Leonard; Stocker, RolandThere is clear evidence of lipoprotein oxidation in atherosclerotic lesions. Animal studies and observational prospective human cohort studies have been interpreted as supporting a role for antioxidants in the prevention of coronary heart disease (CHD). However, firm recommendations to take antioxidant supplements to treat or prevent CHD require evidence derived from randomised controlled studies. In primary prevention studies, low dose ?-tocopherol does not reduce the incidence of coronary events (ATBC study), and ?-carotene either has no effect or increases the incidence of coronary events and cancer death (ATBC, CARET, Physician's Health studies). Secondary preventions, those with smaller populations and shorter duration of follow up have shown some benefit from ?-tocopherol (CHAOS, SPACE), but larger randomised studies indicate no benefit from treatment with ?-tocopherol (HOPE, GISSI, PPP). Recent studies with antioxidant combinations also show no benefit (HATS, MPS). On the basis of these data, supplements of ?-tocopherol and ?-carotene cannot be recommended for the treatment or prevention of CHD. Fundamental and applied research may yet find a role for antioxidant supplements in the treatment of coronary disease. However, this will require positive results from combined antioxidant studies currently in progress, and the targeting of oxidative processes that operate in the artery wall and cause or contribute to disease. 2002 Elsevier Science Ltd. All rights reserved.
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Rolph, Michael S.; Zimmer, Sabine; Bottazzi, Barbara; Garlanda, Cecilia; Mantovani, Alberto; Hansson, Gan K.Elevated plasma levels of the pentraxin protein family member C-reactive protein (CRP) are associated with increased risk of cardiovascular disease in both healthy and high-risk subjects. The long pentraxin family member, pentraxin 3 (PTX3), was recently described. Like CRP, PTX3 is induced by acute inflammatory stimuli and is increased in the blood of patients with acute myocardial infarction. Unlike CRP, it is expressed in a wide range of cell types, but not in hepatocytes. In this study, we have investigated the expression of PTX3 in atherosclerosis. Immunohistochemical staining of advanced atherosclerotic lesions revealed strong expression of PTX3. In contrast, no PTX3 expression was observed in nonatherosclerotic internal mammary arteries. By staining serial sections with cell type- and PTX3-specific antibodies, we observed that PTX3 was produced principally by macrophages and endothelial cells. Infrequent expression by smooth muscle cells was also observed. Our results suggest that PTX3 may contribute to the pathogenesis of atherosclerosis.
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Morin, Bicte; Fu, Shanlin; Wang, Hongjie; Davies, Michael J.; Dean, Roger T.[No abstract available]
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Morgan, Philip E.; Dean, Roger T.; Davies, Michael J.Reaction of certain peptides and proteins with singlet oxygen (generated by visible light in the presence of rose bengal dye) yields long-lived peptide and protein peroxides. Incubation of these peroxides with glyceraldehyde-3-phosphate dehydrogenase, in the absence of added metal ions, results in loss of enzymatic activity. Comparative studies with a range of peroxides have shown that this inhibition is concentration, peroxide, and time dependent, with H<inf>2</inf>O<inf>2</inf> less efficient than some peptide peroxides. Enzyme inhibition correlates with loss of both the peroxide and enzyme thiol residues, with a stoichiometry of two thiols lost per peroxide consumed. Blocking the thiol residues prevents reaction with the peroxide. This stoichiometry, the lack of metal-ion dependence, and the absence of electron paramagnetic resonance (EPR)-detectable species, is consistent with a molecular (nonradical) reaction between the active-site thiol of the enzyme and the peroxide. A number of low-molecular-mass compounds including thiols and ascorbate, but not Trolox C, can prevent inhibition by removing the initial peroxide, or species derived from it. In contrast, glutathione reductase and lactate dehydrogenase are poorly inhibited by these peroxides in the absence of added Fe2+-EDTA. The presence of this metal-ion complex enhanced the inhibition observed with these enzymes consistent with the occurrence of radical-mediated reactions. Overall, these studies demonstrate that singlet oxygen-mediated damage to an initial target protein can result in selective subsequent damage to other proteins, as evidenced by loss of enzymatic activity, via the formation and subsequent reactions of protein peroxides. These reactions may be important in the development of cellular dysfunction as a result of photo-oxidation.
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Hawkins, Clare L.; Rees, Martin D.; Davies, Michael J.Activated phagocytes generate both superoxide radicals via a respiratory burst, and HOCl via the concurrent release of the haem enzyme myeloperoxidase. Amine and amide functions on proteins and carbohydrates are major targets for HOCl, generating chloramines (RNHCl) and chloramides (RC(O)NClR?), which can accumulate to high concentrations ( > 100 ?M). Here we show that superoxide radicals catalyse the decomposition of chloramines and chloramides to reactive nitrogen-centred radicals, and increase the extent of protein fragmentation compared to that observed with either superoxide radicals or HOCl, alone. This synergistic action may be of significance at sites of inflammation, where both superoxide radicals and chloramines/chloramides are formed simultaneously. 2002 Federation of European Biochemical Societies. Published by Elsevier Science B.V. All rights reserved.
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Hawkins, Clare L.; Davies, Michael J.Stimulated monocytes and neutrophils generate hypochlorite (HOCl) via the release of the enzyme myeloperoxidase and hydrogen peroxide. HOCl is a key bactericidal agent, but can also damage host tissue. As there is a strong link between chronic inflammation and some cancers, we have investigated HOCl damage to DNA, RNA, and polynucleotides. Reaction of HOCl with these materials is shown to yield multiple semistable chloramines (RNHCl/RR?NCl), which are the major initial products, and account for 50-95% of the added HOCl. These chloramines decay by thermal and metal-ion catalyzed processes, to give nucleoside-derived, nitrogen-centered, radicals. The latter have been characterized by EPR spin trapping. The propensity for radical formation with polynucleotides is cytidine > adenosine = guanosine > uridine = thymidine. The rates of decay, and yield of radicals formed, are dependent on the nature of the nucleobase on which they are formed, with chloramines formed from ring heterocyclic amine groups being less stable than those formed on exocyclic amines (RNH<inf>2</inf> groups). Evidence is presented for chlorine transfer from the former, kinetically favored, sites to the more thermodynamically favored exocyclic amines. EPR experiments have also provided evidence for the rapid addition of pyrimidine-derived nitrogen-centered radicals to other nucleobases to give dimers and the oxidation of DNA by radicals derived from preformed nucleoside chloramines. Direct reaction of HOCl with plasmid DNA gives rise to single- and double-strand breaks via chloramine-mediated reactions. Preformed nucleoside chloramines also induce plasmid cleavage, though this only occurs to a significant extent with unstable thymidine- and uridine-derived chloramines, where radical formation is rapid. Overall the data rationalize the preferential formation of chlorinated 2?- deoxycytidine and 2?-deoxyadenosine in DNA and suggest that DNA damage induced by HOCl, and preformed chloramines, occurs at sequence-specific sites.
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Sekyere, Eric Owusu; Food, Michael R.; Richardson, Des Raymond[No abstract available]
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Becker, Erika M.; Greer, Judith M.; Po?ka, Prem; Richardson, Des RaymondFriedreich ataxia (FA) is caused by decreased frataxin expression that results in mitochondrial iron (Fe) overload. However, the role of frataxin in mammalian Fe metabolism remains unclear. In this investigation we examined the function of frataxin in Fe metabolism by implementing a well-characterized model of erythroid differentiation, namely, Friend cells induced using dimethyl sulfoxide (DMSO). We have characterized the changes in frataxin expression compared to molecules that play key roles in Fe metabolism (the transferrin receptor [TfR] and the Fe transporter Nramp2) and hemoglobinization (?-globin). DMSO induction of hemoglobinization results in a marked decrease in frataxin gene (Frda) expression and protein levels. To a lesser extent, Nramp2 messenger RNA (mRNA) levels were also decreased on erythroid differentiation, whereas TfR and ?-globin MRNA levels increased. Intracellular Fe depletion using desferrioxamine or pyridoxal isonicotinoyl hydrazone, which chelate cytoplasmic or cytoplasmic and mitochondrial Fe pools, respectively, have no effect on frataxin expression. Furthermore, cytoplasmic or mitochondrial Fe loading of induced Friend cells with ferric ammonium citrate, or the heme synthesis inhibitor, succinylacetone, respectively, also had no effect on frataxin expression. Although frataxin has been suggested by others to be a mitochondrial ferritin, the lack of effect of intracellular Fe levels on frataxin expression is not consistent with an Fe storage role. Significantly, protoporphyrin IX down-regulates frataxin protein levels, suggesting a regulatory role of frataxin in Fe or heme metabolism. Because decreased frataxin expression leads to mitochondrial Fe loading in FA, our data suggest that reduced frataxin expression during erythroid differentiation results in mitochondrial Fe sequestration for heme biosynthesis. 2002 by The American Society of Hematology.
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Medana, Isabelle M.; Tran, Tinh Hien; Day, Nicholas P.J.; Phu, Nguyen Hoan; Mai, Nguyen Thi Hoang; Ly, Van Chuong; Chau, Tran Thi Hong; Taylor, Ann M.; Salahifar, Houta; Stocker, Roland; SMYTHE, George A.; Turner, Gareth D.H.; Farrar, Jeremy James; White, Nicholas J.; Hunt, Nicholas H.A retrospective study of 261 Vietnamese adults with severe malaria was conducted to determine the relationship between cerebrospinal fluid (CSF) levels of metabolites of the kynurenine pathway, the incidence of neurologic complications, and the disease outcome. Three metabolites were measured: The excitotoxin quinolinic acid (QA); the protective receptor antagonist kynurenic acid (KA); and the proinflammatory mediator picolinic acid (PA). These measurements were related prospectively to CSF lactate levels. QA and PA levels were elevated, compared with those of controls. There was no difference in the levels of KA between these groups. Although >40% of malaria patients had QA CSF concentrations in the micromolar range, there was no association with convulsions or depth of coma. Levels of QA and PA were associated significantly with death, but a multivariate analysis suggested that these elevations were a consequence of impaired renal function. CSF lactate remained an independent and significant predictor of poor outcome.
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Gaus, Katharina; Hall, Elizabeth A. H.Short peptides sequences were selected that showed binding selectivity towards healthy or oxidised (unhealthy) low density lipoprotein (LDL), respectively. These were investigated for application in atherosclerosis risk monitoring. Comparison was also made with the LDL receptor ligand repeat peptide (LR5). The peptides were immobilised on a gold surface plasmon resonance surface and LDL binding detected as a shift in the resonance. 3.707 (5.606) LDL/mm2/?g/ml solution LDL were bound on GlySerAspGlu-OH and 6.807 (9.206) LDL/mm2/?g/ml on GlyCystineSerAspGlu, compared with ?108 LDL/mm2/?g/ml on LR5. In this first group, binding of LDL decreased with oxidation level and a good correlation was found between LDL binding and residual amino groups on the apoprotein of the LDL following oxidation, or the change in relative electrophoretic mobility (REM) of LDL. The decrease in binding was 1.107 LDL particles/mm2 per% oxidation for GlySerAspGlu-OH, 1.807 LDL particles/mm2 per% oxidation for GlyCystineSerAspGlu and 2.407 LDL particles/mm2 per% oxidation for LR5. A second group of three peptides were also selected showing increased binding with LDL oxidation: GlyCystineCysCys (1.507 LDL/mm2 per ?g/ml), GlyLysLysCys-SH (107 LDL/mm2 per ?g/ml) and GlyLysLys-OH (5.607 LDL/mm2 per ?g/ml). The latter gave a linear increase in LDL binding with oxidation level (1.207 LDL particles/mm2 per% oxidation). LDL concentration is around 2-3 mg/ml in plasma compared with the low detection levels with this method (1-10 ?g/ml), allowing a strategy to be developed requiring the minimum sample volume and diluting with physiological buffer prior to assay. By using a comparative reading between LDL adsorption on surfaces from the first and second group of peptides (e.g. GlyCystineSerAspGlu and GlyLysLys-OH, respectively), LDL oxidation could be determined without knowledge of LDL concentration. Higher binding was seen on GlyCystineSerAspGlu than GlyLysLys-OH below 30% LDL oxidation, whereas above 30% oxidation the binding on the latter surface was greater. Simple correlation of this form could provide good tests for atherosclerosis risk. 2002 Elsevier Science B.V. All rights reserved.
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Jessup, Wendy K.; Wilson, Paul; Gaus, Katharina; Kritharides, LeonardMacrophages are important participants in the development of atherosclerotic lesions, in cholesterol accumulation, as mediators of the immune response, and as sources of secreted enzymes and growth factors. Besides potentially contributing to local oxidation of lesion lipoproteins, many aspects of macrophage function can be affected by interaction with oxidized lipoproteins. Here we review macrophage responses to oxidized lipoproteins and provide novel data on the effects of a major oxidation product, 7-ketocholesterol, on high-density lipoprotein (HDL) function in cholesterol removal from macrophages. 2002 Elsevier Science Inc. All rights reserved.
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Lyons, Malcolm A.; Maeda, Nobuyuo; Brown, Andrew J.7-Ketocholesterol (7KC) is a major oxysterol found in atherosclerotic plaque and is believed to be derived both endogenously and exogenously (from the diet). Previously, we have demonstrated that subsequent to hepatic lipoprotein uptake, 7KC delivered in a model chylomicron remnant lipid emulsion is metabolised more rapidly and excreted into the intestinal tract and faeces to a much greater extent than simultaneously administered cholesterol. Furthermore, we have shown that human 7KC metabolism is dependent upon sterol 27-hydroxylase (27OHase). In the present work, we utilised a mouse model possessing the null mutation in the sterol 27-hydroxylase gene, Cyp27, to further investigate the metabolism and potential arterial accumulation of 7KC versus cholesterol. Despite the homozygous null mutation in Cyp27 (Cyp27-/-), 7KC was observed to undergo greater metabolism and excretion in the Cyp27-/- animals compared with the wild-type control mice. Six hours post-injection, 7KC levels were greater in aortae from Cyp27-/- mice but by 24 h, there was no significant difference between the knockout and control mice. We conclude that in contrast to humans, mice do not have an absolute requirement for 27OHase in order to metabolise 7KC and must rely on alternative side-chain oxidising pathways. 2002 Elsevier Science B.V. All rights reserved.
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Rodgers, Kenneth John; Wang, Hongjie; Fu, Shanlin; Dean, Roger T.We demonstrate that oxidized amino acids can be incorporated into proteins by protein synthesis. The level of incorporation into protein was dependent on the concentration of oxidized amino acid supplied to the cells. At low levels of incorporation, the oxidized amino acids examined increased the degradation rate of the cell proteins. Degradation of certain proteins containing high levels of DOPA (but not ortho or meta tyrosine) was decreased to below the basal degradation rates suggesting that DOPA may contribute to proteins becoming resistant to proteolysis. Changes in the degradation rates of the oxidized amino acid-containing proteins was shown to have no impact on the degradation rates of native proteins, indicating that the activity of the degradative machinery was not affected. We demonstrate that oxidized proteins are selectively degraded by the proteasomes and provide evidence to suggest that the proteasomes and the endosomal-lysosomal systems may act in sequence as well as in parallel. The incorporation approach, unlike cell studies in which an exogenous oxidant is used, allows the degradation rates of the oxidatively modified proteins to be selectively measured, offering a greater sensitivity as well as greatly reducing toxicity to the cell and avoiding oxidative modification of other cell components. 2002 Elsevier Science Inc.
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Luxford, Catherine; Dean, Roger T.; Davies, Michael J.Exposure of amino acids, peptides and proteins to radicals in the presence of O<inf>2</inf> generates hydroperoxides in a dose-dependent manner. These hydroperoxides are stable in the absence of exogenous catalysts (e.g. heat, light, redox-active transition metal ions), but decompose rapidly in the presence of these agents to give a variety of radicals including alkoxyl (RO), peroxyl (ROO) and carbon-centred (R) species. These radicals are shown to react with DNA to give DNA-protein cross-links and single strand breaks.
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Mashima, Ryuichi; Tilley, L. M.; Siomos, Mary Anne V.; Papalexis, Vicki; Raftery, Mark J.; Stocker, RolandHistidine-rich protein-2 from Plasmodium falciparum (PfHRP2) binds up to 50 molecules of ferri-protoporphyrin IX (FePPIX) (Choi, C. Y., Cerda, J. F., Chu, H. A., Babcock, G. T., and Marletta, M. A. (1999) Biochemistry 38, 16916-16924). We reasoned that the PfHRP2-FePPIX complex has antioxidant properties that could be beneficial to the parasite. Therefore, we examined whether binding to PfHRP2 modulated the redox properties of FePPIX. We observed that PfHRP2 completely inhibited the auto-oxidation of ascorbate mediated by free FeP-PIX. We also investigated the peroxidase activity of Pf-HRP2-FePPIX using 13-hydroperoxy-9,11-octadienoate (18:2-OOH) as substrate. Reaction of PfHRP2-FePPIX with 18:2-OOH in the presence of added reducing agents gave 13-hydroxy-9,11-octadienoate (18:2-OH) as a major product and 13-keto-9,11-octadienoate (18:2=O) and 9,12,13-trihydroxy-10-octadecaenoate as minor products. Binding of FePPIX to PfHRP2 lowered the rate of decomposition of 18:2-OOH and increased the 18:2-OH to 18:2=O ratio. Similar to other authentic peroxidases, phenols, amines, and biological reductants like ascorbate promoted 18:2-OH production, and NaCN inhibited 18:2-OH production. Thioanisole also acted as a reductant and was converted to thioanisole sulfoxide, suggesting formation of compound I during the reaction. These data show that PfHRP2 modulates the redox activity of FePPIX and that the PfHRP2-FePPIX complex may have previously unrecognized antioxidant properties.
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Upston, Joanne M.; Terentis, Andrew C.; Morris, Kathryn; Keaney, John F.; Stocker, RolandOxidative modification of low-density lipoproteins in the arterial wall is a key feature of atherogenesis and widely believed to cause and/or accelerate lesion development. Linked to this is the expectation that vascular antioxidants are depleted during oxidation in vivo. However, whether ?-tocopherol (vitamin E), an important lipid-soluble antioxidant, is depleted early in atherogenesis and can prevent lipid peroxidation in vivo is unresolved. To address this we examined the content of specific configurational isomers (cis/trans) of lipid hydro(pero)xides in lesions, which represent the major non-enzymic oxidation products, as formation and accumulation of cis/trans isomers is influenced by ?-tocopherol in studies in vitro. Concordant with our previous findings that large amounts of oxidized lipid coexist with relatively normal ?-tocopherol levels in human lesions, we now show that cis/trans isomers predominate over other products in human carotid and aortic lesions and in lesion lipoproteins. Further, dietary vitamin E supplementation of rabbits after arterial injury significantly increases both the aortic levels of ?-tocopherol and the overall content of cis/trans isomers. These data are fully consistent with ?-tocopherol acting as a hydrogen donor during lipid oxidation in vivo and suggest that ?-tocopherol does not prevent lipoprotein lipid oxidation in the diseased vessel wall.
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Terentis, Andrew C.; Thomas, Shane R.; Takikawa, Osamu; Littlejohn, Tamantha K.; Truscott, Roger John Willis; Armstrong, Robert S.; Stocker, Syun Ru Yeh RolandIndoleamine 2,3-dioxygenase is a heme enzyme that catalyzes the oxidative degradation of L-Trp and other indoleamines. We have used resonance Raman spectroscopy to characterize the heme environment of purified recombinant human indoleamine 2,3-dioxygenase (hIDO). In the absence of L-Trp, the spectrum of the Fe3+ form displayed six-coordinate, mixed high and low spin character. Addition of L-Trp triggered a transition to predominantly low spin with two Fe-OH- stretching modes identified at 546 and 496 cm-1, suggesting H-bonding between the NH group of the pyrrole ring of L-Trp and heme-bound OH-. The distal pocket of Fe3+ hIDO was explored further by an exogenous heme ligand, CN-; again, binding of L-Trp introduced strong H-bonding and/or steric interactions to the heme-bound CN-. On the other hand, the spectrum of Fe2+ hIDO revealed a five-coordinate and high spin heme with or without L-Trp bound. The proximal Fe-His stretching mode, identified at 236 cm-1, did not shift upon L-Trp addition, indicating that the proximal Fe-His bond strength is not affected by binding of the substrate. The high Fe-His stretching frequency suggests that Fe2+ hIDO has a strong "peroxidase-like" Fe-His bond. Using CO as a structural probe for the distal environment of Fe2+ hIDO revealed that binding of L-Trp in the distal pocket converted IDO to a peroxidase-like enzyme. Binding of L-Trp also caused conformational changes to the heme vinyl groups, which were independent of changes of the spin and coordination state of the heme iron. Together these data indicate that the strong proximal Fe-His bond and the strong H-bonding and/or steric interactions between L-Trp and dioxygen in the distal pocket are likely crucial for the enzymatic activity of hIDO.
