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Figueroa JD, Fuentes-Lemus E, Dorta E, Melin V, Cortés-Ríos J, Faúndez M, Contreras D, Denicola A, Álvarez B, Davies MJ, López-Alarcón C. Quantification of carbonate radical formation by the bicarbonate-dependent peroxidase activity of superoxide dismutase 1 using pyrogallol red bleaching. Redox Biol 2019; 24:101207. [PMID: 31102971 PMCID: PMC6523824 DOI: 10.1016/j.redox.2019.101207] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2019] [Revised: 04/17/2019] [Accepted: 04/23/2019] [Indexed: 01/25/2023] Open
Abstract
Carbonate radicals (CO3•-) are generated by the bicarbonate-dependent peroxidase activity of cytosolic superoxide dismutase (Cu,Zn-SOD, SOD-1). The present work explored the use of bleaching of pyrogallol red (PGR) dye to quantify the rate of CO3•- formation from bovine and human SOD-1 (bSOD-1 and hSOD-1, respectively). This approach was compared to previously reported methods using electron paramagnetic resonance spin trapping with DMPO, and the oxidation of ABTS (2,2-azino-bis(3-ethylbenzothiazoline)-6-sulfonic acid). The kinetics of PGR consumption elicited by CO3•- was followed by visible spectrophotometry. Solutions containing PGR (5–200 μM), SOD-1 (0.3–3 μM), H2O2 (2 mM) in bicarbonate buffer (200 mM, pH 7.4) showed a rapid loss of the PGR absorption band centered at 540 nm. The initial consumption rate (Ri) gave values independent of the initial PGR concentration allowing an estimate to be made of the rate of CO3•- release of 24.6 ± 4.3 μM min−1 for 3 μM bSOD-1. Both bSOD-1 and hSOD-1 showed a similar peroxidase activity, with enzymatic inactivation occurring over a period of 20 min. The single Trp residue (Trp32) present in hSOD-1 was rapidly consumed (initial consumption rate 1.2 ± 0.1 μM min−1) with this occurring more rapidly than hSOD-1 inactivation, suggesting that these processes are not directly related. Added free Trp was rapidly oxidized in competition with PGR. These data indicate that PGR reacts rapidly and efficiently with CO3•- resulting from the peroxidase activity of SOD-1, and that PGR-bleaching is a simple, fast and cheap method to quantify CO3•- release from bSOD-1 and hSOD-1 peroxidase activity. CO3•- are released during the bicarbonate-dependent peroxidase activity of SOD-1. The rate and extent of CO3•- release can be determined by pyrogallol red bleaching. Inactivation of bSOD-1 and hSOD-1 occurs rapidly during the reaction. SOD-1 inactivation is independent of the presence of pyrogallol red. This assay should help elucidate protein oxidation/crosslinking mediated by SOD-1.
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Affiliation(s)
- Juan David Figueroa
- Departamento de Química Física, Facultad de Química y de Farmacia, Pontificia Universidad Católica de Chile, Chile
| | - Eduardo Fuentes-Lemus
- Departamento de Química Física, Facultad de Química y de Farmacia, Pontificia Universidad Católica de Chile, Chile
| | - Eva Dorta
- Departamento de Química Física, Facultad de Química y de Farmacia, Pontificia Universidad Católica de Chile, Chile; Departamento de Nutrición y Ciencia de los Alimentos, Facultad de Farmacia, Universidad Complutense de Madrid, Madrid, Spain
| | - Victoria Melin
- Laboratorio de Recursos Renovables, Facultad de Ciencias Químicas, Centro de Biotecnología, Universidad de Concepción.Chile
| | - Javiera Cortés-Ríos
- Departamento de Farmacia, Facultad de Química y de Farmacia, Pontificia Universidad Católica de Chile, Chile
| | - Mario Faúndez
- Departamento de Farmacia, Facultad de Química y de Farmacia, Pontificia Universidad Católica de Chile, Chile
| | - David Contreras
- Laboratorio de Recursos Renovables, Facultad de Ciencias Químicas, Centro de Biotecnología, Universidad de Concepción.Chile
| | - Ana Denicola
- Laboratorio de Fisicoquímica Biológica, Facultad de Ciencias, Universidad de la República, Uruguay
| | - Beatriz Álvarez
- Laboratorio de Enzimología, Facultad de Ciencias, Universidad de la República, Uruguay
| | - Michael J Davies
- Department of Biomedical Sciences, Panum Institute, University of Copenhagen, Denmark
| | - Camilo López-Alarcón
- Departamento de Química Física, Facultad de Química y de Farmacia, Pontificia Universidad Católica de Chile, Chile.
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Ranguelova K, Ganini D, Bonini MG, London RE, Mason RP. Kinetics of the oxidation of reduced Cu,Zn-superoxide dismutase by peroxymonocarbonate. Free Radic Biol Med 2012; 53:589-94. [PMID: 22569304 PMCID: PMC3408790 DOI: 10.1016/j.freeradbiomed.2012.04.029] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/21/2011] [Revised: 04/11/2012] [Accepted: 04/26/2012] [Indexed: 10/28/2022]
Abstract
Kinetic evidence is reported for the role of the peroxymonocarbonate, HOOCO(2)(-), as an oxidant for reduced Cu,Zn-superoxide dismutase-Cu(I) (SOD1) during the peroxidase activity of the enzyme. The formation of this reactive oxygen species results from the equilibrium between hydrogen peroxide and bicarbonate. Recently, peroxymonocarbonate has been proposed to be a key substrate for reduced SOD1 and has been shown to oxidize SOD1-Cu(I) to SOD1-Cu(II) much faster than H(2)O(2). We have reinvestigated the kinetics of the reaction between SOD1-Cu(I) and HOOCO(2)(-) by using conventional stopped-flow spectrophotometry and obtained a second-order rate constant of k=1600±100M(-1)s(-1) for SOD1-Cu(I) oxidation by HOOCO(2)(-). Our results demonstrate that peroxymonocarbonate oxidizes SOD1-Cu(I) to SOD1-Cu(II) and is in turn reduced to the carbonate anion radical. It is proposed that the dissociation of His61 from the active site Cu(I) in SOD-Cu(I) contributes to this chemistry by facilitating the binding of larger anions, such as peroxymonocarbonate.
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Affiliation(s)
- Kalina Ranguelova
- Laboratory of Pharmacology and Toxicology, NIEHS, National Institutes of Health, Research Triangle Park, NC 27709, USA
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Panov A, Kubalik N, Zinchenko N, Hemendinger R, Dikalov S, Bonkovsky HL. Respiration and ROS production in brain and spinal cord mitochondria of transgenic rats with mutant G93a Cu/Zn-superoxide dismutase gene. Neurobiol Dis 2011; 44:53-62. [PMID: 21745570 DOI: 10.1016/j.nbd.2011.06.003] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/05/2011] [Revised: 05/30/2011] [Accepted: 06/09/2011] [Indexed: 12/14/2022] Open
Abstract
UNLABELLED Mitochondrial dysfunction is involved in the pathogenesis of motor neuron degeneration in the G93A mutant transgenic (tgmSOD1) animal model of ALS. However, it is unknown whether mitochondriopathy is a primary or secondary event. We isolated brain (BM) and spinal cord (SCM) mitochondria from 2 month old presymptomatic tgmSOD1 rats and studied respiration and generation of reactive oxygen species (ROS) using a new metabolic paradigm (Panov et al., Am. J. Physiol., Regul. Integr. Comp. Physiol., 2011). The yields of BM and SCM from tgmSOD1 rats were 27% and 58% lower than normal rats (WT). The rates of the State 3 and State 3U respiration of tgBM and tgSCM were normal with glutamate+pyruvate+malate as substrates but were inhibited with pyruvate+malate in tgBM and glutamate+malate in tgSCM. In tgSCM the State 4 respiration with all substrates was significantly (1.5-2 fold) increased as compared with WT-SCM. Western blot analysis showed that tgSCM had lower contents of complexes III (-60%) and IV (-35%), and the presence of mutated SOD1 protein in both tgBM and tgSCM. With glutamate+pyruvate+malate or succinate+glutamate+pyruvate+malate as substrates, tgBM and tgSCM generated 5-7 fold more ROS than normal mitochondria, and tgSCM generated two times more ROS than tgBM. We show that the major damaging ROS species in tgmSOD1 animals is H(2)O(2). It is known that mutated SOD1, damaged by H(2)O(2), associates with mitochondria, and we suggest that this further increases production of H(2)O(2). We also show that the total tissue calcium content remained normal in the brain but was diminished by 26% in the spinal cord of presymptomatic tgmSOD1 rats. CONCLUSION In tgSCM abnormally high rates of ROS generation, associated with reverse electron transport, result in accelerated mitochondriopathy, and the Ca(2+)-dependent excitotoxic death of motor neurons. Thus mitochondrial dysfunction is a key early element in pathogenesis of motor neuron degeneration in tgmSOD1 rats.
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Affiliation(s)
- Alexander Panov
- Carolinas Neuromuscular/ALS Research Laboratory, Cannon Research Center, Carolinas Medical Center, Charlotte, NC 28203, USA.
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Abreu IA, Cabelli DE. Superoxide dismutases-a review of the metal-associated mechanistic variations. BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS 2009; 1804:263-74. [PMID: 19914406 DOI: 10.1016/j.bbapap.2009.11.005] [Citation(s) in RCA: 316] [Impact Index Per Article: 21.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/03/2009] [Revised: 11/04/2009] [Accepted: 11/05/2009] [Indexed: 10/20/2022]
Abstract
Superoxide dismutases are enzymes that function to catalytically convert superoxide radical to oxygen and hydrogen peroxide. These enzymes carry out catalysis at near diffusion controlled rate constants via a general mechanism that involves the sequential reduction and oxidation of the metal center, with the concomitant oxidation and reduction of superoxide radicals. That the catalytically active metal can be copper, iron, manganese or, recently, nickel is one of the fascinating features of this class of enzymes. In this review, we describe these enzymes in terms of the details of their catalytic properties, with an emphasis on the mechanistic differences between the enzymes. The focus here will be concentrated mainly on two of these enzymes, copper, zinc superoxide dismutase and manganese superoxide dismutase, and some relatively subtle variations in the mechanisms by which they function.
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Affiliation(s)
- Isabel A Abreu
- Plant Genetic Engineering Group, Instituto de Tecnologia Química e Biológica da Universidade Nova de Lisboa, Quinta do Marquês, 2784-505 Oeiras, Portugal
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Medinas DB, Toledo, Jr. JC, Cerchiaro G, do-Amaral AT, de-Rezende L, Malvezzi A, Augusto O. Peroxymonocarbonate and Carbonate Radical Displace the Hydroxyl-like Oxidant in the Sod1 Peroxidase Activity under Physiological Conditions. Chem Res Toxicol 2009; 22:639-48. [DOI: 10.1021/tx800287m] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Danilo B. Medinas
- Departamento de Bioquímica and Departamento de Química Fundamental do Instituto de Química, Universidade de São Paulo, Caixa Postal 26077, CEP 05513-970, São Paulo, Brazil
| | - José C. Toledo, Jr.
- Departamento de Bioquímica and Departamento de Química Fundamental do Instituto de Química, Universidade de São Paulo, Caixa Postal 26077, CEP 05513-970, São Paulo, Brazil
| | - Giselle Cerchiaro
- Departamento de Bioquímica and Departamento de Química Fundamental do Instituto de Química, Universidade de São Paulo, Caixa Postal 26077, CEP 05513-970, São Paulo, Brazil
| | - Antonia T. do-Amaral
- Departamento de Bioquímica and Departamento de Química Fundamental do Instituto de Química, Universidade de São Paulo, Caixa Postal 26077, CEP 05513-970, São Paulo, Brazil
| | - Leandro de-Rezende
- Departamento de Bioquímica and Departamento de Química Fundamental do Instituto de Química, Universidade de São Paulo, Caixa Postal 26077, CEP 05513-970, São Paulo, Brazil
| | - Alberto Malvezzi
- Departamento de Bioquímica and Departamento de Química Fundamental do Instituto de Química, Universidade de São Paulo, Caixa Postal 26077, CEP 05513-970, São Paulo, Brazil
| | - Ohara Augusto
- Departamento de Bioquímica and Departamento de Química Fundamental do Instituto de Química, Universidade de São Paulo, Caixa Postal 26077, CEP 05513-970, São Paulo, Brazil
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Barbosa LF, Garcia CCM, Di Mascio P, de Medeiros MHG. DNA oxidation, strand-breaks and etheno-adducts formation promoted by Cu, Zn-superoxide dismutase–H2O2 in the presence and absence of bicarbonate. Dalton Trans 2009:1450-9. [PMID: 19462668 DOI: 10.1039/b813235f] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Affiliation(s)
- Lívea Fujita Barbosa
- Departamento de Bioquímica, Instituto de Química, Universidade de São Paulo, Av. Prof. Lineu Prestes 748, CEP 05508-900, São Paulo, SP, Brazil
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Ramirez DC, Gomez-Mejiba SE, Corbett JT, Deterding LJ, Tomer KB, Mason RP. Cu,Zn-superoxide dismutase-driven free radical modifications: copper- and carbonate radical anion-initiated protein radical chemistry. Biochem J 2009; 417:341-53. [PMID: 18764780 PMCID: PMC2701971 DOI: 10.1042/bj20070722] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
The understanding of the mechanism, oxidant(s) involved and how and what protein radicals are produced during the reaction of wild-type SOD1 (Cu,Zn-superoxide dismutase) with H2O2 and their fate is incomplete, but a better understanding of the role of this reaction is needed. We have used immuno-spin trapping and MS analysis to study the protein oxidations driven by human (h) and bovine (b) SOD1 when reacting with H2O2 using HSA (human serum albumin) and mBH (mouse brain homogenate) as target models. In order to gain mechanistic information about this reaction, we considered both copper- and CO3(*-) (carbonate radical anion)-initiated protein oxidation. We chose experimental conditions that clearly separated SOD1-driven oxidation via CO(*-) from that initiated by copper released from the SOD1 active site. In the absence of (bi)carbonate, site-specific radical-mediated fragmentation is produced by SOD1 active-site copper. In the presence of (bi)carbonate and DTPA (diethylenetriaminepenta-acetic acid) (to suppress copper chemistry), CO(*-) produced distinct radical sites in both SOD1 and HSA, which caused protein aggregation without causing protein fragmentation. The CO(*-) produced by the reaction of hSOD1 with H2O2 also produced distinctive DMPO (5,5-dimethylpyrroline-N-oxide) nitrone adduct-positive protein bands in the mBH. Finally, we propose a biochemical mechanism to explain CO(*-) production from CO2, enhanced protein radical formation and protection by (bi)carbonate against H2O2-induced fragmentation of the SOD1 active site. Our present study is important for establishing experimental conditions for studying the molecular mechanism and targets of oxidation during the reverse reaction of SOD1 with H2O2; these results are the first step in analysing the critical targets of SOD1-driven oxidation during pathological processes such as neuroinflammation.
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Affiliation(s)
- Dario C. Ramirez
- Free Radical Biology and Aging Program, Oklahoma Medical Research Foundation, Oklahoma City, Oklahoma 73104
| | - Sandra E. Gomez-Mejiba
- Free Radical Biology and Aging Program, Oklahoma Medical Research Foundation, Oklahoma City, Oklahoma 73104
| | - Jean T. Corbett
- Laboratory of Pharmacology, National Institute of Environmental Health Sciences, National Institutes of Health, 111 T.W. Alexander Dr., Research Triangle Park, NC 27709
| | - Leesa J. Deterding
- Laboratory of Structural Biology, National Institute of Environmental Health Sciences, National Institutes of Health, 111 T.W. Alexander Dr., Research Triangle Park, NC 27709
| | - Kenneth B. Tomer
- Laboratory of Structural Biology, National Institute of Environmental Health Sciences, National Institutes of Health, 111 T.W. Alexander Dr., Research Triangle Park, NC 27709
| | - Ronald P. Mason
- Laboratory of Pharmacology, National Institute of Environmental Health Sciences, National Institutes of Health, 111 T.W. Alexander Dr., Research Triangle Park, NC 27709
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Kolla VA, Vavasseur A, Raghavendra AS. Hydrogen peroxide production is an early event during bicarbonate induced stomatal closure in abaxial epidermis of Arabidopsis. PLANTA 2007; 225:1421-9. [PMID: 17160388 DOI: 10.1007/s00425-006-0450-6] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/16/2006] [Accepted: 11/06/2006] [Indexed: 05/12/2023]
Abstract
The presence of 2 mM bicarbonate in the incubation medium induced stomatal closure in abaxial epidermis of Arabidopsis. Exposure to 2 mM bicarbonate elevated the levels of H(2)O(2) in guard cells within 5 min, as indicated by the fluorescent probe, dichlorofluorescein diacetate (H(2)DCF-DA). Bicarbonate-induced stomatal closure as well as H(2)O(2) production were restricted by exogenous catalase or diphenylene iodonium (DPI, an inhibitor of NAD(P)H oxidase). The reduced sensitivity of stomata to bicarbonate and H(2)O(2) production in homozygous atrbohD/F double mutant of Arabidopsis confirmed that NADP(H) oxidase is involved during bicarbonate induced ROS production in guard cells. The production of H(2)O(2) was quicker and greater with ABA than that with bicarbonate. Such pattern of H(2)O(2) production may be one of the reasons for ABA being more effective than bicarbonate, in promoting stomatal closure. Our results demonstrate that H(2)O(2) is an essential secondary messenger during bicarbonate induced stomatal closure in Arabidopsis.
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Affiliation(s)
- V A Kolla
- Department of Plant Sciences, School of Life Sciences, University of Hyderabad, Hyderabad, 500 046, India
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Stopped-flow study of H+ induced CO2 release from a non-peptide analogue of decarboxylase-substrate mimicking cis-[Cr(C2O4)(AaraNH2)(O2CO)]−. TRANSIT METAL CHEM 2006. [DOI: 10.1007/s11243-006-0107-0] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
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Liochev SI, Fridovich I. The role of CO2 in metal-catalyzed peroxidations. J Inorg Biochem 2006; 100:694-6. [PMID: 16500710 DOI: 10.1016/j.jinorgbio.2006.01.030] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2005] [Revised: 01/11/2006] [Accepted: 01/11/2006] [Indexed: 11/17/2022]
Abstract
Transition metals, such as Cu(+2), Mn(+2), and Co(+2), have been seen to catalyze the bicarbonate enhanced oxidation of a variety of substrates by H(2)O(2). In several of these cases it has been demonstrated that CO(2), rather than bicarbonate, is the enhancing species. Mechanisms that are in accord with the data involve a hypervalent state that may be written (MO)(+n), or (MOH)(+n+1), or (M)(+n+2). This metal centered oxidant then oxidizes CO(2) to the carbonate radical; that is then the proximal oxidant of the various substrates. Whether a similar process has in vivo reality remains to be demonstrated.
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Affiliation(s)
- Stefan I Liochev
- The Department of Biochemistry, Box 3711, Duke University Medical Center, Durham, NC 27710, USA
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Abstract
Copper-zinc superoxide dismutase (CuZnSOD, SOD1 protein) is an abundant copper- and zinc-containing protein that is present in the cytosol, nucleus, peroxisomes, and mitochondrial intermembrane space of human cells. Its primary function is to act as an antioxidant enzyme, lowering the steady-state concentration of superoxide, but when mutated, it can also cause disease. Over 100 different mutations have been identified in the sod1 genes of patients diagnosed with the familial form of amyotrophic lateral sclerosis (fALS). These mutations result in a highly diverse group of mutant proteins, some of them very similar to and others enormously different from wild-type SOD1. Despite their differences in properties, each member of this diverse set of mutant proteins causes the same clinical disease, presenting a challenge in formulating hypotheses as to what causes SOD1-associated fALS. In this review, we draw together and summarize information from many laboratories about the characteristics of the individual mutant SOD1 proteins in vivo and in vitro in the hope that it will aid investigators in their search for the cause(s) of SOD1-associated fALS.
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Affiliation(s)
- Joan Selverstone Valentine
- Department of Chemistry and Biochemistry, University of California, Los Angeles, California 90095-1569, USA.
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Liochev SI, Fridovich I. The role of CO2 in cobalt-catalyzed peroxidations. Arch Biochem Biophys 2005; 439:99-104. [PMID: 15946639 DOI: 10.1016/j.abb.2005.05.011] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2005] [Revised: 05/06/2005] [Accepted: 05/08/2005] [Indexed: 11/27/2022]
Abstract
Augmentation, by CO(2)/HCO(3)(-), of Co(II)-catalyzed peroxidations was explored to clarify whether the rate enhancement was due to CO(2) or to HCO(3)(-). The rate of oxidation of NADH by Co(II) plus H(2)O(2), in Tris or phosphate, was markedly enhanced by CO(2)/HCO(3)(-). Phosphate was seen to inhibit the Co(II)-catalyzed peroxidation, probably due to its sequestration of the Co(II). When CO(2) was used, there was an initial burst of NADH oxidation followed by a slower linear rate. The presence of carbonic anhydrase eliminated this initial burst; establishing that CO(2) rather than HCO(3)(-) was the species responsible for the observed rate enhancements. Both kinetic and spectral data indicated that Co(II) was converted by H(2)O(2) into a less active form from which Co(II) could be regenerated. This less active form absorbed in both the UV and visible regions, and is assumed to be a peroxy bridged binuclear complex. The rate of formation of this absorbing form was increased by HCO(3)(-)/CO(2). A minimal mechanism consistent with these observations is proposed.
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Affiliation(s)
- Stefan I Liochev
- The Department of Biochemistry, Duke University Medical Center, Durham, NC 27710, USA
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Ramirez DC, Mejiba SEG, Mason RP. Copper-catalyzed Protein Oxidation and Its Modulation by Carbon Dioxide. J Biol Chem 2005; 280:27402-11. [PMID: 15905164 DOI: 10.1074/jbc.m504241200] [Citation(s) in RCA: 60] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
It is well known that hydrogen peroxide (H2O2)-induced copper-catalyzed fragmentation of proteins follows a site-specific oxidative mechanism mediated by hydroxyl radical-like species (i.e. Cu(I)O, Cu(II)/*OH or Cu(III)) that ends in increased carbonyl formation and protein fragmentation. We have found that the nitrone spin trap DMPO (5,5-dimethyl-1-pyrroline N-oxide) prevented such processes by trapping human serum albumin (HSA)-centered radicals, in situ and in real time, before they reacted with oxygen. When (bi)carbonate (CO2, H2CO3, HCO3- and CO3(-2)) was added to the reaction mixture, it blocked fragmentation mediated by hydroxyl radical-like species but enhanced DMPO-trappable radical sites in HSA. In the past, this effect would have been explained by oxidation of (bi)carbonate to a carbonate radical anion (CO3*) by a bound hydroxyl radical-like species. We now propose that the CO3* radical is formed by the reduction of HOOCO2- (a complex of H2O2 with CO2) by the protein-Cu(I) complex. CO3* diffuses and produces more DMPO-trappable radical sites but does not fragment HSA. We were also able, for the first time, to detect discrete but highly specific H2O2-induced copper-catalyzed CO3*-mediated induction of DMPO-trappable protein radicals in functioning RAW 264.7 macrophages. We conclude that carbon dioxide modulates H2O2-induced copper-catalyzed oxidative damage to proteins by preventing site-specific fragmentation and enhancing DMPO-trappable protein radicals in functioning cells. The pathophysiological significance of our findings is discussed.
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Affiliation(s)
- Dario C Ramirez
- Laboratory of Pharmacology and Chemistry, NIEHS, National Institutes of Health, Research Triangle Park, North Carolina 27709, USA.
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