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Shimada A, Tsukihara T, Yoshikawa S. Recent progress in experimental studies on the catalytic mechanism of cytochrome c oxidase. Front Chem 2023; 11:1108190. [PMID: 37214485 PMCID: PMC10194837 DOI: 10.3389/fchem.2023.1108190] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2022] [Accepted: 04/18/2023] [Indexed: 05/24/2023] Open
Abstract
Cytochrome c oxidase (CcO) reduces molecular oxygen (O2) to water, coupled with a proton pump from the N-side to the P-side, by receiving four electrons sequentially from the P-side to the O2-reduction site-including Fea3 and CuB-via the two low potential metal sites; CuA and Fea. The catalytic cycle includes six intermediates as follows, R (Fea3 2+, CuB 1+, Tyr244OH), A (Fea3 2+-O2, CuB 1+, Tyr244OH), Pm (Fea3 4+ = O2-, CuB 2+-OH-, Tyr244O•), F (Fea3 4+ = O2-, CuB 2+-OH-, Tyr244OH), O (Fea3 3+-OH-, CuB 2+-OH-, Tyr244OH), and E (Fea3 3+-OH-, CuB 1+-H2O, Tyr244OH). CcO has three proton conducting pathways, D, K, and H. The D and K pathways connect the N-side surface with the O2-reduction site, while the H-pathway is located across the protein from the N-side to the P-side. The proton pump is driven by electrostatic interactions between the protons to be pumped and the net positive charges created during the O2 reduction. Two different proton pump proposals, each including either the D-pathway or H-pathway as the proton pumping site, were proposed approximately 30 years ago and continue to be under serious debate. In our view, the progress in understanding the reaction mechanism of CcO has been critically rate-limited by the resolution of its X-ray crystallographic structure. The improvement of the resolutions of the oxidized/reduced bovine CcO up to 1.5/1.6 Å resolution in 2016 provided a breakthrough in the understanding of the reaction mechanism of CcO. In this review, experimental studies on the reaction mechanism of CcO before the appearance of the 1.5/1.6 Å resolution X-ray structures are summarized as a background description. Following the summary, we will review the recent (since 2016) experimental findings which have significantly improved our understanding of the reaction mechanism of CcO including: 1) redox coupled structural changes of bovine CcO; 2) X-ray structures of all six intermediates; 3) spectroscopic findings on the intermediate species including the Tyr244 radical in the Pm form, a peroxide-bound form between the A and Pm forms, and Fr, a one-electron reduced F-form; 4) time resolved X-ray structural changes during the photolysis of CO-bound fully reduced CcO using XFEL; 5) a simulation analysis for the Pm→Pr→F transition.
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Affiliation(s)
- Atsuhiro Shimada
- Department of Applied Life Science, Faculty of Applied Biological Sciences, Gifu University, Gifu, Japan
| | - Tomitake Tsukihara
- Department of Life Science, Graduate School of Science, University of Hyogo, Hyogo, Japan
- Institute for Protein Research, Osaka University, Osaka, Japan
| | - Shinya Yoshikawa
- Department of Life Science, Graduate School of Science, University of Hyogo, Hyogo, Japan
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2
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Lin W, Qiao C, Hu J, Wei Q, Xu T. Conserved role of ATP synthase in mammalian cilia. Exp Cell Res 2021; 401:112520. [PMID: 33639177 DOI: 10.1016/j.yexcr.2021.112520] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2020] [Revised: 02/09/2021] [Accepted: 02/11/2021] [Indexed: 10/22/2022]
Abstract
We previously found that ATP synthases localize to male-specific sensory cilia and control the ciliary response by regulating polycystin signalling in Caenorhabditis elegans. Herein, we discovered that the ciliary localization of ATP synthase is evolutionarily conserved in mammals. We showed that the ATP synthase subunit F1β is colocalized with the cilia marker acetylated α-tubulin in both mammalian renal epithelial cells (MDCK) and normal mouse cholangiocytes (NMCs). Treatment with ATP synthase inhibitor oligomycin impaired ciliogenesis in MDCK cells, and F1β was co-immunoprecipitated with PKD2 in mammalian cells. Our study provides evidence for the evolutionarily conserved localization of ATP synthase in cilia from worm to mammals. Defects in ATP synthase can lead to ciliary dysfunction, which may be a potential mechanism of polycystic kidney disease.
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Affiliation(s)
- Wenjun Lin
- Department of Nephrology, Shanghai Jiao Tong University Affiliated Sixth People's Hospital, Shanghai, 200233, China
| | - Cheng Qiao
- Department of Nephrology, Shanghai Jiao Tong University Affiliated Sixth People's Hospital, Shanghai, 200233, China
| | - Jinghua Hu
- Department of Biochemistry and Molecular Biology, Mayo Clinic, Rochester, MN, USA
| | - Qing Wei
- Center for Energy Metabolism and Reproduction, Institute of Biomedicine and Biotechnology, Shenzhen Institutes of Advanced Technology, Chinese Academy of Sciences (CAS), Shenzhen, 518055, China
| | - Tao Xu
- Department of Nephrology, Shanghai Jiao Tong University Affiliated Sixth People's Hospital, Shanghai, 200233, China.
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3
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Adam SM, Wijeratne GB, Rogler PJ, Diaz DE, Quist DA, Liu JJ, Karlin KD. Synthetic Fe/Cu Complexes: Toward Understanding Heme-Copper Oxidase Structure and Function. Chem Rev 2018; 118:10840-11022. [PMID: 30372042 PMCID: PMC6360144 DOI: 10.1021/acs.chemrev.8b00074] [Citation(s) in RCA: 145] [Impact Index Per Article: 24.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
Heme-copper oxidases (HCOs) are terminal enzymes on the mitochondrial or bacterial respiratory electron transport chain, which utilize a unique heterobinuclear active site to catalyze the 4H+/4e- reduction of dioxygen to water. This process involves a proton-coupled electron transfer (PCET) from a tyrosine (phenolic) residue and additional redox events coupled to transmembrane proton pumping and ATP synthesis. Given that HCOs are large, complex, membrane-bound enzymes, bioinspired synthetic model chemistry is a promising approach to better understand heme-Cu-mediated dioxygen reduction, including the details of proton and electron movements. This review encompasses important aspects of heme-O2 and copper-O2 (bio)chemistries as they relate to the design and interpretation of small molecule model systems and provides perspectives from fundamental coordination chemistry, which can be applied to the understanding of HCO activity. We focus on recent advancements from studies of heme-Cu models, evaluating experimental and computational results, which highlight important fundamental structure-function relationships. Finally, we provide an outlook for future potential contributions from synthetic inorganic chemistry and discuss their implications with relevance to biological O2-reduction.
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Affiliation(s)
- Suzanne M. Adam
- Department of Chemistry, Johns Hopkins University, Baltimore, Maryland 21218, United States
| | - Gayan B. Wijeratne
- Department of Chemistry, Johns Hopkins University, Baltimore, Maryland 21218, United States
| | - Patrick J. Rogler
- Department of Chemistry, Johns Hopkins University, Baltimore, Maryland 21218, United States
| | - Daniel E. Diaz
- Department of Chemistry, Johns Hopkins University, Baltimore, Maryland 21218, United States
| | - David A. Quist
- Department of Chemistry, Johns Hopkins University, Baltimore, Maryland 21218, United States
| | - Jeffrey J. Liu
- Department of Chemistry, Johns Hopkins University, Baltimore, Maryland 21218, United States
| | - Kenneth D. Karlin
- Department of Chemistry, Johns Hopkins University, Baltimore, Maryland 21218, United States
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4
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Calcium ions inhibit reduction of heme a in bovine cytochrome c oxidase. FEBS Lett 2015; 589:3853-8. [PMID: 26611345 DOI: 10.1016/j.febslet.2015.11.023] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2015] [Revised: 11/15/2015] [Accepted: 11/16/2015] [Indexed: 01/14/2023]
Abstract
The effect of Ca(2+) on the rate of heme a reduction by dithionite and hexaammineruthenium (RuAm) was studied in the cyanide-complexed bovine cytochrome oxidase (CcO). The rate of heme a reduction is proportional to RuAm concentration below 300 μM with kv of 0.53×10(6) M(-1) s(-1). Ca(2+) inhibits the rate of heme a reduction by dithionite by ∼25%. As the reaction speeds up with increased concentrations of RuAm, the inhibition by Ca(2+) disappears. The inhibition of heme a reduction may contribute to recently described partial inhibition of CcO by Ca(2+) in the enzymatic assays. The inhibitory effect of Ca(2+) on heme a reduction indicates that ET through heme a may be coupled to proton movement in the exit part of the proton channel H.
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5
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Yu Y, Cui C, Liu X, Petrik ID, Wang J, Lu Y. A Designed Metalloenzyme Achieving the Catalytic Rate of a Native Enzyme. J Am Chem Soc 2015; 137:11570-3. [PMID: 26318313 PMCID: PMC4676421 DOI: 10.1021/jacs.5b07119] [Citation(s) in RCA: 63] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
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Terminal
oxidases catalyze four-electron reduction of oxygen to
water, and the energy harvested is utilized to drive the synthesis
of adenosine triphosphate. While much effort has been made to design
a catalyst mimicking the function of terminal oxidases, most biomimetic
catalysts have much lower activity than native oxidases. Herein we
report a designed oxidase in myoglobin with an O2 reduction
rate (52 s–1) comparable to that of a native cytochrome
(cyt) cbb3 oxidase (50 s–1) under identical conditions. We achieved this goal by engineering
more favorable electrostatic interactions between a functional oxidase
model designed in sperm whale myoglobin and its native redox partner,
cyt b5, resulting in a 400-fold electron
transfer (ET) rate enhancement. Achieving high activity equivalent
to that of native enzymes in a designed metalloenzyme offers deeper
insight into the roles of tunable processes such as ET in oxidase
activity and enzymatic function and may extend into applications such
as more efficient oxygen reduction reaction catalysts for biofuel
cells.
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Affiliation(s)
| | | | - Xiaohong Liu
- Laboratory of Non-coding RNA, Institute of Biophysics, Chinese Academy of Sciences , 15 Datun Road, Chaoyang District, Beijing 100101, P. R. China
| | | | - Jiangyun Wang
- Laboratory of Non-coding RNA, Institute of Biophysics, Chinese Academy of Sciences , 15 Datun Road, Chaoyang District, Beijing 100101, P. R. China
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Affiliation(s)
- Shinya Yoshikawa
- Picobiology Institute, Graduate
School of Life Science, University of Hyogo, Kamigohri Akoh Hyogo, 678-1297, Japan
| | - Atsuhiro Shimada
- Picobiology Institute, Graduate
School of Life Science, University of Hyogo, Kamigohri Akoh Hyogo, 678-1297, Japan
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7
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Bhagi-Damodaran A, Petrik ID, Marshall NM, Robinson H, Lu Y. Systematic tuning of heme redox potentials and its effects on O2 reduction rates in a designed oxidase in myoglobin. J Am Chem Soc 2014; 136:11882-5. [PMID: 25076049 PMCID: PMC4151708 DOI: 10.1021/ja5054863] [Citation(s) in RCA: 68] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2014] [Indexed: 11/28/2022]
Abstract
Cytochrome c Oxidase (CcO) is known to catalyze the reduction of O2 to H2O efficiently with a much lower overpotential than most other O2 reduction catalysts. However, methods by which the enzyme fine-tunes the reduction potential (E°) of its active site and the corresponding influence on the O2 reduction activity are not well understood. In this work, we report systematic tuning of the heme E° in a functional model of CcO in myoglobin containing three histidines and one tyrosine in the distal pocket of heme. By removing hydrogen-bonding interactions between Ser92 and the proximal His ligand and a heme propionate, and increasing hydrophobicity of the heme pocket through Ser92Ala mutation, we have increased the heme E° from 95 ± 2 to 123 ± 3 mV. Additionally, replacing the native heme b in the CcO mimic with heme a analogs, diacetyl, monoformyl, and diformyl hemes, that posses electron-withdrawing groups, resulted in higher E° values of 175 ± 5, 210 ± 6, and 320 ± 10 mV, respectively. Furthermore, O2 consumption studies on these CcO mimics revealed a strong enhancement in O2 reduction rates with increasing heme E°. Such methods of tuning the heme E° through a combination of secondary sphere mutations and heme substitutions can be applied to tune E° of other heme proteins, allowing for comprehensive investigations of the relationship between E° and enzymatic activity.
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Affiliation(s)
- Ambika Bhagi-Damodaran
- Department
of Chemistry, University of Illinois, Urbana−Champaign, Urbana, Illinois 61801, United States
| | - Igor D. Petrik
- Department
of Chemistry, University of Illinois, Urbana−Champaign, Urbana, Illinois 61801, United States
| | - Nicholas M. Marshall
- Department
of Chemistry, University of Illinois, Urbana−Champaign, Urbana, Illinois 61801, United States
| | - Howard Robinson
- Department
of Biology, Brookhaven National Laboratory, Upton, New York 11973, United States
| | - Yi Lu
- Department
of Chemistry, University of Illinois, Urbana−Champaign, Urbana, Illinois 61801, United States
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Vygodina TV, Dyuba AV, Konstantinov AA. Effect of calcium ions on electron transfer between hemes a and a 3 in cytochrome c oxidase. BIOCHEMISTRY (MOSCOW) 2012; 77:901-9. [DOI: 10.1134/s0006297912080111] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
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9
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Gupta KJ, Igamberdiev AU. The anoxic plant mitochondrion as a nitrite: NO reductase. Mitochondrion 2011; 11:537-43. [PMID: 21406251 DOI: 10.1016/j.mito.2011.03.005] [Citation(s) in RCA: 108] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2010] [Revised: 02/16/2011] [Accepted: 03/04/2011] [Indexed: 12/30/2022]
Abstract
Under the conditions of oxygen deprivation, accumulating nitrite can be reduced in the mitochondrial electron transport chain forming free radical nitric oxide (NO). By reducing nitrite to NO, plant mitochondria preserve the capacity to oxidize external NADH and NADPH and retain a limited power for ATP synthesis complementing glycolytic ATP production. NO participates in O(2) balance in mitochondria by competitively inhibiting cytochrome c oxidase which can oxidize it to nitrite when oxygen concentration increases. Some of the NO escapes to the cytosol, where the efficient scavenging system involving non-symbiotic hemoglobin oxygenates NO to nitrate and supports continuous anaerobic turnover of nitrogen species.
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Affiliation(s)
- Kapuganti J Gupta
- Department of Plant Physiology, University of Rostock, Albert Einstein Str. 3, D-10859, Germany.
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Igamberdiev AU, Bykova NV, Shah JK, Hill RD. Anoxic nitric oxide cycling in plants: participating reactions and possible mechanisms. PHYSIOLOGIA PLANTARUM 2010; 138:393-404. [PMID: 19929898 DOI: 10.1111/j.1399-3054.2009.01314.x] [Citation(s) in RCA: 62] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/20/2023]
Abstract
At sufficiently low oxygen concentrations, hemeproteins are deoxygenated and become capable of reducing nitrite to nitric oxide (NO), in a reversal of the reaction in which NO is converted to nitrate or nitrite by oxygenated hemeproteins. The maximum rates of NO production depend on the oxygen avidity. The hemeproteins with the highest avidity, such as hexacoordinate hemoglobins, retain oxygen even under anoxic conditions resulting in their being extremely effective NO scavengers but essentially incapable of producing NO. Deoxyhemeprotein-related NO production can be observed in mitochondria (at the levels of cytochrome c oxidase, cytochrome c, complex III and possibly other sites), in plasma membrane, cytosol, endoplasmic reticulum and peroxisomes. In mitochondria, the use of nitrite as an alternative electron acceptor can contribute to a limited rate of ATP synthesis. Non-heme metal-containing proteins such as nitrate reductase and xanthine oxidase can also be involved in NO production. This will result in a strong anoxic redox flux of nitrogen through the hemoglobin-NO cycle involving nitrate reductase, nitrite: NO reductase, and NO dioxygenase. In normoxic conditions, NO is produced in very low quantities, mainly for signaling purposes and this nitrogen cycling is inoperative.
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Affiliation(s)
- Abir U Igamberdiev
- Department of Biology, Memorial University of Newfoundland, St. John's, NL, A1B 3X9, Canada.
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11
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The steady-state mechanism of cytochrome c oxidase: redox interactions between metal centres. Biochem J 2009; 422:237-46. [DOI: 10.1042/bj20082220] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
The steady-state behaviour of isolated mammalian cytochrome c oxidase was examined by increasing the rate of reduction of cytochrome c. Under these conditions the enzyme's 605 (haem a), 655 (haem a3/CuB) and 830 (CuA) nm spectral features behaved as if they were at near equilibrium with cytochrome c (550 nm). This has implications for non-invasive tissue measurements using visible (550, 605 and 655 nm) and near-IR (830 nm) light. The oxidized species represented by the 655 nm band is bleached by the presence of oxygen intermediates P and F (where P is characterized by an absorbance spectrum at 607 nm relative to the oxidized enzyme and F is characterized by an absorbance spectrum at 580 nm relative to the oxidized enzyme) or by reduction of haem a3 or CuB. However, at these ambient oxygen levels (far above the enzyme Km), the populations of reduced haem a3 and the oxygen intermediates were very low (<10%). We therefore interpret 655 nm changes as reduction of the otherwise spectrally invisible CuB centre. We present a model where small anti-cooperative redox interactions occur between haem a–CuA–CuB (steady-state potential ranges: CuA, 212–258 mV; haem a, 254–281 mV; CuB, 227–272 mV). Contrary to static equilibrium measurements, in the catalytic steady state there are no high potential redox centres (>300 mV). We find that the overall reaction is correctly described by the classical model in which the Michaelis intermediate is a ferrocytochrome c–enzyme complex. However, the oxidation of ferrocytochrome c in this complex is not the sole rate-determining step. Turnover is instead dependent upon electron transfer from haem a to haem a3, but the haem a potential closely matches cytochrome c at all times.
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Chandran K, Aggarwal D, Migrino RQ, Joseph J, McAllister D, Konorev EA, Antholine WE, Zielonka J, Srinivasan S, Avadhani NG, Kalyanaraman B. Doxorubicin inactivates myocardial cytochrome c oxidase in rats: cardioprotection by Mito-Q. Biophys J 2009; 96:1388-98. [PMID: 19217856 DOI: 10.1016/j.bpj.2008.10.042] [Citation(s) in RCA: 134] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2008] [Accepted: 10/09/2008] [Indexed: 12/23/2022] Open
Abstract
Doxorubicin (DOX) is used for treating various cancers. Its clinical use is, however, limited by its dose-limiting cardiomyopathy. The exact mechanism of DOX-induced cardiomyopathy still remains unknown. The goals were to investigate the molecular mechanism of DOX-induced cardiomyopathy and cardioprotection by mitoquinone (Mito-Q), a triphenylphosphonium-conjugated analog of coenzyme Q, using a rat model. Rats were treated with DOX, Mito-Q, and DOX plus Mito-Q for 12 weeks. The left ventricular function as measured by two-dimensional echocardiography decreased in DOX-treated rats but was preserved during Mito-Q plus DOX treatment. Using low-temperature ex vivo electron paramagnetic resonance (EPR), a time-dependent decrease in heme signal was detected in heart tissues isolated from rats administered with a cumulative dose of DOX. DOX attenuated the EPR signals characteristic of the exchange interaction between cytochrome c oxidase (CcO)-Fe(III) heme a3 and CuB. DOX and Mito-Q together restored these EPR signals and the CcO activity in heart tissues. DOX strongly downregulated the stable expression of the CcO subunits II and Va and had a slight inhibitory effect on CcO subunit I gene expression. Mito-Q restored CcO subunit II and Va expressions in DOX-treated rats. These results suggest a novel cardioprotection mechanism by Mito-Q during DOX-induced cardiomyopathy involving CcO.
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Affiliation(s)
- Karunakaran Chandran
- Department of Biophysics and Free Radical Research Center, Medical College of Wisconsin, Milwaukee, Wisconsin, USA
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Igamberdiev AU, Hill RD. Plant mitochondrial function during anaerobiosis. ANNALS OF BOTANY 2009; 103:259-68. [PMID: 18586697 PMCID: PMC2707300 DOI: 10.1093/aob/mcn100] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/28/2008] [Revised: 04/29/2008] [Accepted: 05/21/2008] [Indexed: 05/17/2023]
Abstract
BACKGROUND Under hypoxic conditions, plant mitochondria preserve the capacity to oxidize external NADH, NADPH and tricarboxylic acid cycle substrates. Nitrite serves as an alternative electron acceptor at the level of cytochrome oxidase, with possibly complex III and the alternative oxidase also being involved. Nitric oxide is a significant product of the reaction, which has a high affinity for cytochrome c oxidase, inhibiting it. The excess NO is scavenged by hypoxically induced class 1 haemoglobin in the reaction involving ascorbate. SCOPE By using nitrite, mitochondria retain a limited capacity for ATP synthesis. NADH, produced from glycolysis during anaerobiosis and oxidized in the mitochondrial electron transport chain, should shift the composition of metabolites formed during anaerobiosis with increased conversion of pyruvate to alanine and greater involvement of other transamination reactions, such as those involving gamma-aminobutyric acid formation. CONCLUSIONS Anaerobic mitochondrial metabolism may have a more significant role than previously thought in alleviating the effects of anoxia on plant cells. There is a need to re-examine mitochondrial carbon and nitrogen metabolism under anoxia to establish the extent of this involvement.
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Affiliation(s)
- Abir U. Igamberdiev
- Department of Biology, Memorial University of Newfoundland, St John's, NL, Canada, A1B 3X9
| | - Robert D. Hill
- Department of Plant Science, University of Manitoba, Winnipeg, MB, Canada, R3T 2N2
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Cvetkov TL, Prochaska LJ. Biophysical and biochemical characterization of reconstituted and purified Rhodobacter sphaeroides cytochrome c oxidase in phospholipid vesicles sheds insight into its functional oligomeric structure. Protein Expr Purif 2007; 56:189-96. [PMID: 17910921 DOI: 10.1016/j.pep.2007.07.012] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2007] [Revised: 07/16/2007] [Accepted: 07/17/2007] [Indexed: 11/18/2022]
Abstract
Discontinuous sucrose gradient ultracentrifugation was used to separate liposomes containing Rhodobacter sphaeroides cytochrome c oxidase (pCOV) from liposomes devoid of the enzyme, and the biophysical and biochemical properties of pCOV were compared to unpurified liposomes containing cytochrome c oxidase (COV). Isolated and purified R. sphaeroides cytochrome c oxidase (COX) was reconstituted into asolectin phospholipid vesicles by cholate dialysis, and this preparation was purified further on a discontinuous sucrose gradient to isolate only those vesicles which contained the enzyme (pCOV). After centrifugation at 300,000g for 22h, 80% of the enzyme recovered was in a single band. The number of COX molecules per pCOV liposome was estimated by measuring the visible absorbance spectrum of cytochrome c oxidase (for heme aa(3)) and inorganic phosphate concentration (for phospholipid). The number of COX molecules incorporated per pCOV was estimated to be approximately one (0.72+/-0.19-1.09+/-0.28). The pCOV exhibited similar physical properties as COV; respiratory control ratios (indicators of endogenous proton permeability) and maximum enzymatic turnover number at pH 7.4 were comparable (6.0+/-1.3 and 535+/-130s(-1)). Furthermore, proton pumping activities of the pCOV were at least 70% of COV, indicating that discontinuous sucrose gradient centrifugation is a useful technique for functional experiments in R. sphaeroides cytochrome c oxidase. Our results suggest that the monomeric form of R. sphaeroides COX when reconstituted into a phospholipid bilayer is completely functionally active in its ability to perform electron transfer and proton pumping activities of the enzyme.
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Affiliation(s)
- Teresa L Cvetkov
- Department of Biochemistry and Molecular Biology, Boonshoft School of Medicine and College of Science and Mathematics, Wright State University, Dayton, OH 45435, USA
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