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Abstract
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This review focuses on the type
A cytochrome c oxidases (CcO), which
are found in all mitochondria
and also in several aerobic bacteria. CcO catalyzes
the respiratory reduction of dioxygen (O2) to water by
an intriguing mechanism, the details of which are fairly well understood
today as a result of research for over four decades. Perhaps even
more intriguingly, the membrane-bound CcO couples
the O2 reduction chemistry to translocation of protons
across the membrane, thus contributing to generation of the electrochemical
proton gradient that is used to drive the synthesis of ATP as catalyzed
by the rotary ATP synthase in the same membrane. After reviewing the
structure of the core subunits of CcO, the active
site, and the transfer paths of electrons, protons, oxygen, and water,
we describe the states of the catalytic cycle and point out the few
remaining uncertainties. Finally, we discuss the mechanism of proton
translocation and the controversies in that area that still prevail.
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Affiliation(s)
- Mårten Wikström
- Institute of Biotechnology , University of Helsinki , P.O. Box 56 , Helsinki FI-00014 , Finland
| | - Klaas Krab
- Department of Molecular Cell Physiology , Vrije Universiteit , P.O. Box 7161 , Amsterdam 1007 MC , The Netherlands
| | - Vivek Sharma
- Institute of Biotechnology , University of Helsinki , P.O. Box 56 , Helsinki FI-00014 , Finland.,Department of Physics , University of Helsinki , P.O. Box 64 , Helsinki FI-00014 , Finland
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2
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Lankelma J, Kooi B, Krab K, Dorsman JC, Joenje H, Westerhoff HV. A reason for intermittent fasting to suppress the awakening of dormant breast tumors. Biosystems 2014; 127:1-6. [PMID: 25448890 DOI: 10.1016/j.biosystems.2014.11.001] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2014] [Revised: 10/25/2014] [Accepted: 11/01/2014] [Indexed: 12/21/2022]
Abstract
For their growth, dormant tumors, which lack angiogenesis may critically depend on gradients of nutrients and oxygen from the nearest blood vessel. Because for oxygen depletion the distance from the nearest blood vessel to depletion will generally be shorter than for glucose depletion, such tumors will contain anoxic living tumor cells. These cells are dangerous, because they are capable of inducing angiogenesis, which will "wake up" the tumor. Anoxic cells are dependent on anaerobic glucose breakdown for ATP generation. The local extracellular glucose concentration gradient is determined by the blood glucose concentration and by consumption by cells closer to the nearest blood vessel. The blood glucose concentration can be lowered by 20-40% during fasting. We calculated that glucose supply to the potentially hazardous anoxic cells can thereby be reduced significantly, resulting in cell death specifically of the anoxic tumor cells. We hypothesize that intermittent fasting will help to reduce the incidence of tumor relapse via reducing the number of anoxic tumor cells and tumor awakening.
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Affiliation(s)
- Jan Lankelma
- Department of Molecular Cell Physiology, VU University, De Boelelaan 1085, Room G-226a, 1081 HV Amsterdam, The Netherlands.
| | - Bob Kooi
- Department of Theoretical Biology, VU University, De Boelelaan 1085, 1081HV Amsterdam, The Netherlands
| | - Klaas Krab
- Department of Molecular Cell Physiology, VU University, De Boelelaan 1085, Room G-226a, 1081 HV Amsterdam, The Netherlands
| | - Josephine C Dorsman
- Department of Clinical Genetics, VU University Medical Center, Van der Boechorststraat 7, 1081 BT Amsterdam, The Netherlands
| | - Hans Joenje
- Department of Clinical Genetics, VU University Medical Center, Van der Boechorststraat 7, 1081 BT Amsterdam, The Netherlands
| | - Hans V Westerhoff
- Department of Molecular Cell Physiology, VU University, De Boelelaan 1085, Room G-226a, 1081 HV Amsterdam, The Netherlands; Synthetic Systems Biology, SILS, University of Amsterdam and Manchester Centre for Integrative Systems Biology, The University of Manchester, UK
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3
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Boogerd FC, Ma H, Bruggeman FJ, van Heeswijk WC, García-Contreras R, Molenaar D, Krab K, Westerhoff HV. AmtB-mediated NH3
transport in prokaryotes must be active and as a consequence regulation of transport by GlnK is mandatory to limit futile cycling of NH4+/NH3. FEBS Lett 2010; 585:23-8. [DOI: 10.1016/j.febslet.2010.11.055] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/27/2010] [Revised: 11/29/2010] [Accepted: 11/29/2010] [Indexed: 12/19/2022]
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Härdin HM, Zagaris A, Krab K, Westerhoff HV. Simplified yet highly accurate enzyme kinetics for cases of low substrate concentrations. FEBS J 2009; 276:5491-506. [DOI: 10.1111/j.1742-4658.2009.07233.x] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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Ciapaite J, Nauciene Z, Baniene R, Wagner MJ, Krab K, Mildaziene V. Modular kinetic analysis reveals differences in Cd2+ and Cu2+ ion-induced impairment of oxidative phosphorylation in liver. FEBS J 2009; 276:3656-68. [DOI: 10.1111/j.1742-4658.2009.07084.x] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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Wagner AM, Krab K, Wagner MJ, Moore AL. Regulation of thermogenesis in flowering Araceae: the role of the alternative oxidase. Biochim Biophys Acta 2008; 1777:993-1000. [PMID: 18440298 DOI: 10.1016/j.bbabio.2008.04.001] [Citation(s) in RCA: 64] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/03/2008] [Revised: 03/31/2008] [Accepted: 04/01/2008] [Indexed: 11/24/2022]
Abstract
The inflorescences of several members of the Arum lily family warm up during flowering and are able to maintain their temperature at a constant level, relatively independent of the ambient temperature. The heat is generated via a mitochondrial respiratory pathway that is distinct from the cytochrome chain and involves a cyanide-resistant alternative oxidase (AOX). In this paper we have used flux control analysis to investigate the influence of temperature on the rate of respiration through both cytochrome and alternative oxidases in mitochondria isolated from the appendices of intact thermogenic Arum maculatum inflorescences. Results are presented which indicate that at low temperatures, the dehydrogenases are almost in full control of respiration but as the temperature increases flux control shifts to the AOX. On the basis of these results a simple model of thermoregulation is presented that is applicable to all species of thermogenic plants. The model takes into account the temperature characteristics of the separate components of the plant mitochondrial respiratory chain and the control of each process. We propose that 1) in all aroid flowers AOX assumes almost complete control over respiration, 2) the temperature profile of AOX explains the reversed relationship between ambient temperature and respiration in thermoregulating Arum flowers, 3) the thermoregulation process is the same in all species and 4) variations in inflorescence temperatures can easily be explained by variations in AOX protein concentrations.
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Affiliation(s)
- Anneke M Wagner
- Institute of Molecular Cell Biology, VU Universiteit, de Boelelaan 1087, 1081 HV Amsterdam, The Netherlands
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7
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van Boxtel AL, Kamstra JH, Cenijn PH, Pieterse B, Wagner JM, Antink M, Krab K, van der Burg B, Marsh G, Brouwer A, Legler J. Microarray analysis reveals a mechanism of phenolic polybrominated diphenylether toxicity in zebrafish. Environ Sci Technol 2008; 42:1773-1779. [PMID: 18441834 DOI: 10.1021/es0720863] [Citation(s) in RCA: 52] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/26/2023]
Abstract
Polybrominated diphenylethers (PBDEs) are ubiquitous in the environment, with the lower brominated congener 2,2',4,4'-tetrabromodiphenylether (BDE47) among the most prevalent. The phenolic PBDE, 6-hydroxy-BDE47 (6-OH-BDE47) is both an important metabolite formed by in vivo metabolism of BDE47 and a natural product produced by marine organisms such as algae. Although this compound has been detected in humans and wildlife, including fish, virtually nothing is known of its in vivo toxicity. Here we report that 6-OH-BDE47 is acutely toxic in developing and adult zebrafish at concentrations in the nanomolar (nM) range. To identify possible mechanisms of toxicity, we used microarray analysis as a diagnostic tool. Zebrafish embryonic fibroblast (PAC2) cells were exposed to 6-OH-BDE47, BDE47, and the methoxylated metabolite 6-MeO-BDE47. These experiments revealed that 6-OH-BDE47 alters the expression of genes involved in proton transport and carbohydrate metabolism. These findings, combined with the acute toxicity, suggested that 6-OH-BDE47 causes disruption of oxidative phosphorylation (OXPHOS).Therefore, we further investigated the effect of 6-OH-BDE47 on OXPHOS in zebrafish mitochondria. Results show unequivocally that this compound is a potent uncoupler of OXPHOS and is an inhibitor of complex II of the electron transport chain. This study provides the first evidence of the in vivo toxicity and an important potential mechanism of toxicity of an environmentally relevant phenolic PBDE of both anthropogenic and natural origin. The results of this study emphasize the need for further investigation on the presence and toxicity of this class of polybrominated compounds.
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Affiliation(s)
- Antonius L van Boxtel
- Institute for Environmental Studies and Department of Molecular Cell Physiology, Faculty of Earth and Life Sciences, VU University, Amsterdam, The Netherlands
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Westerhoff HV, Kolodkin A, Conradie R, Wilkinson SJ, Bruggeman FJ, Krab K, van Schuppen JH, Hardin H, Bakker BM, Moné MJ, Rybakova KN, Eijken M, van Leeuwen HJP, Snoep JL. Systems biology towards life in silico: mathematics of the control of living cells. J Math Biol 2008; 58:7-34. [PMID: 18278498 DOI: 10.1007/s00285-008-0160-8] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2007] [Revised: 01/11/2008] [Indexed: 12/13/2022]
Abstract
Systems Biology is the science that aims to understand how biological function absent from macromolecules in isolation, arises when they are components of their system. Dedicated to the memory of Reinhart Heinrich, this paper discusses the origin and evolution of the new part of systems biology that relates to metabolic and signal-transduction pathways and extends mathematical biology so as to address postgenomic experimental reality. Various approaches to modeling the dynamics generated by metabolic and signal-transduction pathways are compared. The silicon cell approach aims to describe the intracellular network of interest precisely, by numerically integrating the precise rate equations that characterize the ways macromolecules' interact with each other. The non-equilibrium thermodynamic or 'lin-log' approach approximates the enzyme rate equations in terms of linear functions of the logarithms of the concentrations. Biochemical Systems Analysis approximates in terms of power laws. Importantly all these approaches link system behavior to molecular interaction properties. The latter two do this less precisely but enable analytical solutions. By limiting the questions asked, to optimal flux patterns, or to control of fluxes and concentrations around the (patho)physiological state, Flux Balance Analysis and Metabolic/Hierarchical Control Analysis again enable analytical solutions. Both the silicon cell approach and Metabolic/Hierarchical Control Analysis are able to highlight where and how system function derives from molecular interactions. The latter approach has also discovered a set of fundamental principles underlying the control of biological systems. The new law that relates concentration control to control by time is illustrated for an important signal transduction pathway, i.e. nuclear hormone receptor signaling such as relevant to bone formation. It is envisaged that there is much more Mathematical Biology to be discovered in the area between molecules and Life.
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Affiliation(s)
- Hans V Westerhoff
- Molecular Cell Physiology, Institute of Molecular Cell Biology, Netherlands Institute for Systems Biology, Faculty of Earth and Life Sciences, Vrije Universiteit, De Boelelaan 1085, 1081 HV, Amsterdam, The Netherlands.
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Abstract
Multiple sequence alignments are often used for the identification of key specificity-determining residues within protein families. We present a web server implementation of the Sequence Harmony (SH) method previously introduced. SH accurately detects subfamily specific positions from a multiple alignment by scoring compositional differences between subfamilies, without imposing conservation. The SH web server allows a quick selection of subtype specific sites from a multiple alignment given a subfamily grouping. In addition, it allows the predicted sites to be directly mapped onto a protein structure and displayed. We demonstrate the use of the SH server using the family of plant mitochondrial alternative oxidases (AOX). In addition, we illustrate the usefulness of combining sequence and structural information by showing that the predicted sites are clustered into a few distinct regions in an AOX homology model. The SH web server can be accessed at www.ibi.vu.nl/programs/seqharmwww.
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Affiliation(s)
- K. Anton Feenstra
- Centre for Integrative Bioinformatics VU (IBIVU) and Institute of Molecular Cell Biology, Vrije Universiteit Amsterdam, De Boelelaan 1081A, 1081 HV Amsterdam, The Netherlands
| | - Walter Pirovano
- Centre for Integrative Bioinformatics VU (IBIVU) and Institute of Molecular Cell Biology, Vrije Universiteit Amsterdam, De Boelelaan 1081A, 1081 HV Amsterdam, The Netherlands
| | - Klaas Krab
- Centre for Integrative Bioinformatics VU (IBIVU) and Institute of Molecular Cell Biology, Vrije Universiteit Amsterdam, De Boelelaan 1081A, 1081 HV Amsterdam, The Netherlands
| | - Jaap Heringa
- Centre for Integrative Bioinformatics VU (IBIVU) and Institute of Molecular Cell Biology, Vrije Universiteit Amsterdam, De Boelelaan 1081A, 1081 HV Amsterdam, The Netherlands
- *To whom correspondence should be addressed. +31 20 598 7649+31 20 598 7653
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Ciapaite J, van Bezu J, van Eikenhorst G, Bakker SJL, Teerlink T, Diamant M, Heine RJ, Krab K, Westerhoff HV, Schalkwijk CG. Palmitate and oleate have distinct effects on the inflammatory phenotype of human endothelial cells. Biochim Biophys Acta Mol Cell Biol Lipids 2006; 1771:147-54. [PMID: 17240190 DOI: 10.1016/j.bbalip.2006.12.005] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2006] [Revised: 12/13/2006] [Accepted: 12/13/2006] [Indexed: 11/22/2022]
Abstract
Free fatty acids may create a state of continuous and progressive damaging to the vascular wall manifested by endothelial dysfunction. In this study we determine the mechanisms by which fatty acids palmitate (C16:0) and oleate (C18:1) affect intracellular long chain acyl-CoA (LCAC) content, energy metabolism, cell survival and proliferation and activation of NF-kappaB in cultured endothelial cells. A 48-h exposure of human umbilical vein endothelial cells (HUVEC) to 0.5 mM palmitate or 0.5 mM oleate increased total long chain acyl-CoA (LCAC) content 1.7 and 2 fold, respectively and decreased ATP(total)/ADP(total) ratio by 26+/-5% (mean+/-SEM) and 15+/-2%, respectively, which was prevented by the acyl-CoA synthetase inhibitor triacsin C. Furthermore, palmitate inhibited cell proliferation by 34+/-5%, while oleate stimulated it by 12+/-2%. alpha-Tocopherol fully and triacsin C partially abolished the effect of palmitate on cell proliferation. Palmitate and oleate increased caspase-3 activity 3.2 and 1.4 fold, respectively. Palmitate-induced caspase-3 activation was prevented by triacsin C and slightly reduced by alpha-tocopherol and by the de novo ceramide synthesis inhibitor fumonisin B(1). Both fatty acids induced antioxidant-sensitive nuclear translocation of NF-kappaB after 72 h, but not after 48 h. In conclusion, we showed that fatty acids influence different aspects of HUVEC function resulting in amongst other activation of apoptotic and inflammatory pathways. Our results indicate that the effects depend on the fatty acid type and may be related to accumulation of LCAC.
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Affiliation(s)
- Jolita Ciapaite
- Department of Molecular Cell Physiology, Institute for Molecular Cell Biology, VU University, Amsterdam, The Netherlands
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Ciapaite J, Bakker SJL, Van Eikenhorst G, Wagner MJ, Teerlink T, Schalkwijk CG, Fodor M, Ouwens DM, Diamant M, Heine RJ, Westerhoff HV, Krab K. Functioning of oxidative phosphorylation in liver mitochondria of high-fat diet fed rats. Biochim Biophys Acta Mol Basis Dis 2006; 1772:307-16. [PMID: 17184976 DOI: 10.1016/j.bbadis.2006.10.018] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2006] [Revised: 10/22/2006] [Accepted: 10/23/2006] [Indexed: 01/07/2023]
Abstract
We proposed that inhibition of mitochondrial adenine nucleotide translocator (ANT) by long chain acyl-CoA (LCAC) underlies the mechanism associating obesity and type 2 diabetes. Here we test that after long-term exposure to a high-fat diet (HFD): (i) there is no adaptation of the mitochondrial compartment that would hinder such ANT inhibition, and (ii) ANT has significant control of the relevant aspects of oxidative phosphorylation. After 7 weeks, HFD induced a 24+/-6% increase in hepatic LCAC concentration and accumulation of the oxidative stress marker N(epsilon)-(carboxymethyl)lysine. HFD did not significantly affect mitochondrial copy number, oxygen uptake, membrane potential (Deltapsi), ADP/O ratio, and the content of coenzyme Q(9), cytochromes b and a+a(3). Modular kinetic analysis showed that the kinetics of substrate oxidation, phosphorylation, proton leak, ATP-production and ATP-consumption were not influenced significantly. After HFD-feeding ANT exerted considerable control over oxygen uptake (control coefficient C=0.14) and phosphorylation fluxes (C=0.15), extra- (C=0.23) and intramitochondrial (C=-0.56) ATP/ADP ratios, and Deltapsi (C=-0.11). We conclude that although HFD induces accumulation of LCAC and N(epsilon)-(carboxymethyl)lysine, oxidative phosphorylation does not adapt to these metabolic challenges. Furthermore, ANT retains control of fluxes and intermediates, making inhibition of this enzyme a more probable link between obesity and type 2 diabetes.
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Affiliation(s)
- Jolita Ciapaite
- Department of Molecular Cell Physiology, Institute for Molecular Cell Biology, Faculty of Earth and Life Sciences, VU University, Amsterdam, The Netherlands.
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Ciapaite J, Bakker SJL, Diamant M, van Eikenhorst G, Heine RJ, Westerhoff HV, Krab K. Metabolic control of mitochondrial properties by adenine nucleotide translocator determines palmitoyl-CoA effects. Implications for a mechanism linking obesity and type 2 diabetes. FEBS J 2006; 273:5288-302. [PMID: 17059463 DOI: 10.1111/j.1742-4658.2006.05523.x] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
Inhibition of the mitochondrial adenine nucleotide translocator (ANT) by long-chain acyl-CoA esters has been proposed to contribute to cellular dysfunction in obesity and type 2 diabetes by increasing formation of reactive oxygen species and adenosine via effects on the coenzyme Q redox state, mitochondrial membrane potential (Deltapsi) and cytosolic ATP concentrations. We here show that 5 microm palmitoyl-CoA increases the ratio of reduced to oxidized coenzyme Q (QH(2)/Q) by 42 +/- 9%, Deltapsi by 13 +/- 1 mV (9%), and the intramitochondrial ATP/ADP ratio by 352 +/- 34%, and decreases the extramitochondrial ATP/ADP ratio by 63 +/- 4% in actively phosphorylating mitochondria. The latter reduction is expected to translate into a 24% higher extramitochondrial AMP concentration. Furthermore, palmitoyl-CoA induced concentration-dependent H(2)O(2) formation, which can only partly be explained by its effect on Deltapsi. Although all measured fluxes and intermediate concentrations were affected by palmitoyl-CoA, modular kinetic analysis revealed that this resulted mainly from inhibition of the ANT. Through Metabolic Control Analysis, we then determined to what extent the ANT controls the investigated mitochondrial properties. Under steady-state conditions, the ANT moderately controlled oxygen uptake (control coefficient C = 0.13) and phosphorylation (C = 0.14) flux. It controlled intramitochondrial (C = -0.70) and extramitochondrial ATP/ADP ratios (C = 0.23) more strongly, whereas the control exerted over the QH(2)/Q ratio (C = -0.04) and Deltapsi (C = -0.01) was small. Quantitative assessment of the effects of palmitoyl-CoA showed that the mitochondrial properties that were most strongly controlled by the ANT were affected the most. Our observations suggest that long-chain acyl-CoA esters may contribute to cellular dysfunction in obesity and type 2 diabetes through effects on cellular energy metabolism and production of reactive oxygen species.
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Affiliation(s)
- Jolita Ciapaite
- Department of Molecular Cell Physiology, Institute for Molecular Cell Biology, Faculty of Earth and Life Sciences, VU University, Amsterdam, the Netherlands.
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Kasimova MR, Grigiene J, Krab K, Hagedorn PH, Flyvbjerg H, Andersen PE, Møller IM. The free NADH concentration is kept constant in plant mitochondria under different metabolic conditions. Plant Cell 2006; 18:688-98. [PMID: 16461578 PMCID: PMC1383643 DOI: 10.1105/tpc.105.039354] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/06/2023]
Abstract
The reduced coenzyme NADH plays a central role in mitochondrial respiratory metabolism. However, reports on the amount of free NADH in mitochondria are sparse and contradictory. We first determined the emission spectrum of NADH bound to proteins using isothermal titration calorimetry combined with fluorescence spectroscopy. The NADH content of actively respiring mitochondria (from potato tubers [Solanum tuberosum cv Bintje]) in different metabolic states was then measured by spectral decomposition analysis of fluorescence emission spectra. Most of the mitochondrial NADH is bound to proteins, and the amount is low in state 3 (substrate + ADP present) and high in state 2 (only substrate present) and state 4 (substrate + ATP). By contrast, the amount of free NADH is low but relatively constant, even increasing a little in state 3. Using modeling, we show that these results can be explained by a 2.5- to 3-fold weaker average binding of NADH to mitochondrial protein in state 3 compared with state 4. This indicates that there is a specific mechanism for free NADH homeostasis and that the concentration of free NADH in the mitochondrial matrix per se does not play a regulatory role in mitochondrial metabolism. These findings have far-reaching consequences for the interpretation of cellular metabolism.
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Affiliation(s)
- Marina R Kasimova
- Optics and Plasma Research Department, Risø National Laboratory, DK-4000 Roskilde, Denmark
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Abstract
Mitochondria, isolated from heterotrophic Euglena gracilis , have cyanide-resistant alternative oxidase (AOX) in their respiratory chain. Cells cultured under a variety of oxidative stress conditions (exposure to cyanide, cold, or H2O2) increased the AOX capacity in mitochondria and cells, although it was significant only under cold stress; AOX sensitivity to inhibitors was also increased by cold and cyanide stress. The value of AOX maximal activity reached 50% of total respiration below 20 degrees C, whereas AOX full activity was only 10-30% of total respiration above 20 degrees C. The optimum pH for AOX activity was 6.5 and for the cytochrome pathway was 7.3. GMP, AMP, pyruvate, or DTT did not alter AOX activity. The reduction level of the quinone pool was higher in mitochondria from cold-stressed than from control cells; furthermore, the content of reduced glutathione was lower in cold-stressed cells. Growth in the presence of an AOX inhibitor was not affected in control cells, whereas in cold-stressed cells, growth was diminished by 50%. Cyanide diminished growth in control cells by 50%, but in cold-stressed cells this inhibitor was ineffective. The data suggest that AOX activity is part of the cellular response to oxidative stress in Euglena .
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15
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Ciapaite J, Van Eikenhorst G, Bakker SJL, Diamant M, Heine RJ, Wagner MJ, Westerhoff HV, Krab K. Modular kinetic analysis of the adenine nucleotide translocator-mediated effects of palmitoyl-CoA on the oxidative phosphorylation in isolated rat liver mitochondria. Diabetes 2005; 54:944-51. [PMID: 15793231 DOI: 10.2337/diabetes.54.4.944] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
To test whether long-chain fatty acyl-CoA esters link obesity with type 2 diabetes through inhibition of the mitochondrial adenine nucleotide translocator, we applied a system-biology approach, dual modular kinetic analysis, with mitochondrial membrane potential (Deltapsi) and the fraction of matrix ATP as intermediates. We found that 5 mumol/l palmitoyl-CoA inhibited adenine nucleotide translocator, without direct effect on other components of oxidative phosphorylation. Indirect effects depended on how oxidative phosphorylation was regulated. When the electron donor and phosphate acceptor were in excess, and the mitochondrial "work" flux was allowed to vary, palmitoyl-CoA decreased phosphorylation flux by 38% and the fraction of ATP in the medium by 39%. Deltapsi increased by 15 mV, and the fraction of matrix ATP increased by 46%. Palmitoyl-CoA had a stronger effect when the flux through the mitochondrial electron transfer chain was maintained constant: Deltapsi increased by 27 mV, and the fraction of matrix ATP increased 2.6 times. When oxidative phosphorylation flux was kept constant by adjusting the rate using hexokinase, Deltapsi and the fraction of ATP were not affected. Palmitoyl-CoA increased the extramitochondrial AMP concentration significantly. The effects of palmitoyl-CoA in our model system support the proposed mechanism linking obesity and type 2 diabetes through an effect on adenine nucleotide translocator.
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Affiliation(s)
- Jolita Ciapaite
- Department of Molecular Cell Physiology, Institute for Molecular Cell Biology, BioCenter Amsterdam, Faculty of EarthLife Sciences, Vrije Universiteit, De Boelelaan 1085, NL-1081 HV Amsterdam, the Netherlands
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16
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Brady NR, Elmore SP, van Beek JJHGM, Krab K, Courtoy PJ, Hue L, Westerhoff HV. Coordinated behavior of mitochondria in both space and time: a reactive oxygen species-activated wave of mitochondrial depolarization. Biophys J 2005; 87:2022-34. [PMID: 15345578 PMCID: PMC1304605 DOI: 10.1529/biophysj.103.035097] [Citation(s) in RCA: 101] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
Reactive oxygen species (ROS) can trigger a transient burst of mitochondrial ROS production via ROS activation of the mitochondrial permeability transition pore (MPTP), a phenomenon termed ROS-induced ROS release (RIRR). The goal of this study was to investigate if the generation of ROS in a discrete region of a cardiomyocyte could serve to propagate RIRR-mediated mitochondrial depolarizations throughout a cell. Our experiments revealed that localized RIRR activated either RIRR-mediated fluctuations in mitochondrial membrane potential (time period: 3-10 min) or a traveling wave of depolarization of the cell's mitochondria (velocity: approximately 5 microm/min). Both phenomena appeared to be mediated by the mitochondrial permeability transition pore and eventually encompassed the majority of the mitochondrial population of both isolated rat and rabbit cardiomyocytes. Furthermore, depolarization was often reversible; the waves of depolarization were then followed by a rapid (approximately 40 microm/min) repolarization wave of the mitochondria. We show that the RIRR can function to communicate the mitochondrial permeability transition from one mitochondrion to another in the isolated adult cardiomyocyte.
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Affiliation(s)
- Nathan R Brady
- Department of Molecular Cell Physiology, The Centre for Research on BioComplex Systems, BioCentrum Amsterdam, NL-1081 HV, Amsterdam, The Netherlands
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Kongas O, Wagner MJ, ter Veld F, Nicolay K, van Beek JHGM, Krab K. The mitochondrial outer membrane is not a major diffusion barrier for ADP in mouse heart skinned fibre bundles. Pflugers Arch 2004; 447:840-4. [PMID: 14722773 DOI: 10.1007/s00424-003-1214-9] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/09/2003] [Accepted: 11/05/2003] [Indexed: 12/01/2022]
Abstract
The response of mitochondrial oxygen consumption to ADP in saponin-skinned cardiac fibre bundles has an apparent Km an order of magnitude higher than that in isolated mitochondria. Here we report that incubating skinned cardiac fibre bundles from wild-type mice or double-knockout mice lacking both cytosolic and mitochondrial creatine kinase (CK) with CK and creatine or with yeast hexokinase and glucose as extramitochondrial ADP-producing systems decreases the apparent Km of the bundles for ADP severalfold. We conclude that the affinity of mitochondria for ADP in mouse heart is of the same order of magnitude as that of isolated mitochondria, while the high apparent Km of the bundles is caused by diffusion gradients outside the mitochondria.
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Affiliation(s)
- Olav Kongas
- Department of Mechanics and Applied Mathematics, Institute of Cybernetics, Tallinn Technical University, Akadeemia 21, 12618 Tallinn, Estonia.
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Ciapaite J, van Eikenhorst G, Krab K. Application of modular control analysis to inhibition of the adenine nucleotide translocator by palmitoyl-CoA. Mol Biol Rep 2003; 29:13-6. [PMID: 12241043 DOI: 10.1023/a:1020385714555] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Modular kinetic analysis was used to characterize inhibition of adenine nucleotide translocation by palmitoyl-CoA in isolated rat-liver mitochondria. To this purpose, oxidative phosphorylation has been divided into two modules with the fraction of matrix ATP as linking intermediate. The adenine nucleotide translocator is the matrix ATP-consuming module and the remainder of oxidative phosphorylation (ATP synthesis, respiratory chain and transport of phosphates and respiratory substrate) is the matrix ATP-producing module. We found that palmitoyl-CoA inhibits ATP-consuming module (ANT) and has no effect on ATP-producing module. There were no significant differences between kinetic curves obtained with oligomycin and myxothiazol, inhibitors that have opposite effect on membrane potential, suggesting that the use of the fraction of matrix ATP as the only intermediate is a good approximation. A new method has been used to determine the fraction of ATP in the mitochondrial matrix.
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Affiliation(s)
- J Ciapaite
- Department of Molecular Cell physiology, Faculty of Earth and Life Sciences, Vrije Universiteit, Amsterdam, The Netherlands
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19
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Mildaziene V, Nauciene Z, Baniene R, Demin O, Krab K. Analysis of effects of 2,2',5,5'-tetrachlorobiphenyl on the flux control in oxidative phosphorylation system in rat liver mitochondria. Mol Biol Rep 2002; 29:35-40. [PMID: 12241071 DOI: 10.1023/a:1020346100442] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Modular kinetic analysis reveals that the environmental pollutant 2,2',5,5'-tetrachlorobiphenyl (2,2',5,5'-TCB) affects a large number of steps in oxidative phosphorylation in rat liver mitochondria. 2,2',5,5'-TCB increases membrane permeability to ions, and inhibits NADH dehydrogenase, cytochrome bc1, cytochrome oxidase (all in the respiratory chain) and ATP-synthase (in the phosphorylation subsystem). Surprisingly, flux control distribution does not change. A kinetic model for oxidative phosphorylation was used to simulate these findings, and it was found that combined large changes in the processes indicated indeed left the flux control largely unchanged. In addition, computational analysis with the model indicated that the adenine nucleotide translocator might be inhibited by 2,2',5,5'-TCB.
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20
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Mildaziene V, Nauciene Z, Krab K. The targets of 2,2',5,5'-tetrachlorobiphenyl in the respiratory chain of rat liver mitochondria revealed by modular kinetic analysis. Mol Biol Rep 2002; 29:31-4. [PMID: 12241070 DOI: 10.1023/a:1020394016372] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
The response of the respiratory subsystem of oxidative phosphorylation to the environmental pollutant, 2,2',5,5'-tetrachlorobiphenyl (2,2',5,5'-TCB) was investigated by modular kinetic approach. The effects of 20 microM 2,2',5,5'-TCB on the activity of the respiratory chain modules in rat liver mitochondria oxidizing succinate (+ rotenone) in state 3 were assessed. The toxin inhibited the rate of respiration by 23%. Analysis around cytochrome c revealed that 2,2',5,5'-TCB inhibited both cytochrome c-oxidizing and reducing modules. The toxin inhibited also CoQ-oxidizing module, however it did not affect the kinetics of CoQ-reducing module. Taken together, these data indicated that 2,2',5,5'-TCB inhibited cytochrome bc1 but had no effect on succinate dehydrogenase.
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Koefoed S, Otten M, Koebmann B, Bruggeman F, Bakker B, Snoep J, Krab K, van Spanning R, van Verseveld H, Jensen P, Koster J, Westerhoff H. A turbo engine with automatic transmission? How to marry chemicomotion to the subtleties and robustness of life. Biochim Biophys Acta 2002; 1555:75-82. [PMID: 12206895 DOI: 10.1016/s0005-2728(02)00258-x] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Most genomes are much more complex than required for the minimum chemistry of life. Evolution has selected sophistication more than life itself. Could this also apply to bioenergetics? We first examine mechanisms through which bioenergetics could deliver sophistication. We illustrate possible benefits of the turbo-charging of catabolic pathways, of loose coupling, low-gear catabolism, automatic transmission in energy coupling, and of homeostasis. Mechanisms for such phenomena may reside at the level of individual proton pumps, or consist of rerouting of electrons over parallel pathways. The mechanisms may be confined to preexisting components, or involve the plasticity of gene expression that is so characteristic of most living organisms. These possible benefits lead us to the conjecture that also bioenergetics has evolved more for sophistication than for necessity. We next discuss a hitherto unresolved enigma, i.e. that bioenergetics does not seem to be critical for the physiological state. To decide on how critical bioenergetics is, we quantified the control exerted by catabolism on important physiological functions such as growth rate and growth yield. We also determined whether a growth inhibition mostly affected bioenergetics (catabolism) or anabolism; if ATP increases with growth rate, then growth should be considered energy (catabolism) limited. The experimental results for Escherichia coli pinpoint the enigma: its energy metabolism (catabolism) is not critical for growth rate. These results might suggest that because it has no direct control over cell function, bioenergetics is unimportant. Paradoxically however, in biology, highly important mechanisms tend to have little control on cell function, precisely because of that importance. Sophistication in terms of homeostatic mechanisms has evolved to guarantee robustness of the most important functions: The most important mechanisms are redundant in biology. Bioenergetics may be an excellent example of this paradox, in line with the above conjecture. It may be highly important and sophisticated. We then discuss work that has begun to focus on the sophistication of bioenergetics. Homeostasis of the energetics of DNA structure in E. coli is extensive. It relies both on preexisting components and on responsive gene expression. The vastly parallel electron-transfer network of Paracoccus denitrificans engages in sophisticated dynamic and hierarchical regulation. The growth yield of the organism can depend on which terminal oxidases are active. Effective proton translocation may vary due to rerouting of electrons. We conclude that much sophistication of bioenergetics will be discovered in this era of functional genomics.
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Kongas O, Yuen TL, Wagner MJ, Van Beek JHGM, Krab K. High K(m) of oxidative phosphorylation for ADP in skinned muscle fibers: where does it stem from? Am J Physiol Cell Physiol 2002; 283:C743-51. [PMID: 12176731 DOI: 10.1152/ajpcell.00101.2002] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Mitochondria in saponin-skinned cardiac fiber bundles were reported to have an order of magnitude lower apparent affinity to ADP than isolated mitochondria. Although ADP was measured outside the bundles, it was thought that the low affinity was not caused by diffusion gradients because of relatively short diffusion distances. Here we test the hypothesis that considerable ADP diffusion gradients exist and can be diminished by increasing the intrafiber ADP production rate. We increased the ADP-producing activity in rat heart skinned fiber bundles by incubating with 100 IU/ml yeast hexokinase and glucose. Consequently, we observed a significant decrease of the apparent Michaelis constant (K(m)) to ADP of the respiration rate of bundles from 216 +/- 59 to 50 +/- 9 microM. Fitting the results with a mathematical model, we estimated the K(m) of mitochondria in the bundles to be 25 microM. We conclude that the affinity to ADP of in situ mitochondria in heart is of the same order of magnitude as that of isolated mitochondria.
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Affiliation(s)
- Olav Kongas
- Laboratory for Physiology, Institute for Cardiovascular Research, Vrije Universiteit Medical Center 1081 BT Amsterdam, The Netherlands.
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23
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Affourtit C, Krab K, Leach GR, Whitehouse DG, Moore AL. New insights into the regulation of plant succinate dehydrogenase. On the role of the protonmotive force. J Biol Chem 2001; 276:32567-74. [PMID: 11350973 DOI: 10.1074/jbc.m103111200] [Citation(s) in RCA: 42] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Regulation of succinate dehydrogenase was investigated using tightly coupled potato tuber mitochondria in a novel fashion by simultaneously measuring the oxygen uptake rate and the ubiquinone (Q) reduction level. We found that the activation level of the enzyme is unambiguously reflected by the kinetic dependence of the succinate oxidation rate upon the Q-redox poise. Kinetic results indicated that succinate dehydrogenase is activated by both ATP (K(1/2) approximately 3 microm) and ADP. The carboxyatractyloside insensitivity of these stimulatory effects indicated that they occur at the cytoplasmic side of the mitochondrial inner membrane. Importantly, our novel approach revealed that the enzyme is also activated by oligomycin (K(1/2) approximately 16 nm). Time-resolved kinetic measurements of succinate dehydrogenase activation by succinate furthermore revealed that the activity of the enzyme is negatively affected by potassium. The succinate-induced activation (+/-K(+)) is prevented by the presence of an uncoupler. Together these results demonstrate that in vitro activity of succinate dehydrogenase is modulated by the protonmotive force. We speculate that the widely recognized activation of the enzyme by adenine nucleotides in plants is mediated in this manner. A mechanism that could account for such regulation is suggested and ramifications for its in vivo relevance are discussed.
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Affiliation(s)
- C Affourtit
- Department of Biochemistry, School of Biological Sciences, University of Sussex, Falmer, Brighton BN1 9QG, United Kingdom.
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24
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Abstract
Plant mitochondria are characterised by the presence of both phosphorylating (cytochrome) and non-phosphorylating (alternative) respiratory pathways, the relative activities of which directly affect the efficiency of mitochondrial energy conservation. Different approaches to study the regulation of the partitioning of reducing equivalents between these routes are critically reviewed. Furthermore, an updated view is provided regarding the understanding of plant mitochondrial respiration in terms of metabolic control. We emphasise the extent to which kinetic modelling and 'top-down' metabolic control analysis improve the insight in phenomena related to plant mitochondrial respiration. This is illustrated with an example regarding the affinity of the plant alternative oxidase for oxygen.
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Affiliation(s)
- C Affourtit
- Department of Biochemistry, University of Sussex, Falmer, Brighton, UK.
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25
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Krab K, Wagner MJ, Wagner AM, Moller IM. Identification of the site where the electron transfer chain of plant mitochondria is stimulated by electrostatic charge screening. Eur J Biochem 2000; 267:869-76. [PMID: 10651825 DOI: 10.1046/j.1432-1327.2000.01065.x] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Modular kinetic analysis was used to determine the sites in plant mitochondria where charge-screening stimulates the rate of electron transfer from external NAD(P)H to oxygen. In mitochondria isolated from potato (Solanum tuberosum L.) tuber callus, stimulation of the rate of oxygen uptake was accompanied by a decrease in the steady-state reduction level of coenzyme Q, and by a small decrease in the steady-state reduction level of cytochrome c. Modular kinetic analysis around coenzyme Q revealed that stimulation of the rate was due to stimulation of quinol oxidation via the cytochrome pathway (cytochrome bc1, cytochrome c and cytochrome c oxidase). It was not a consequence of any effect on quinone reduction (by external NADH or NADPH dehydrogenase). This explains the salt-induced decrease in the steady-state reduction level of coenzyme Q. Analysis around cytochrome c revealed that stimulation by salts was due to a dual effect on the respiratory chain. The kinetic curves for the oxidation and reduction pathways of cytochrome c revealed that they were both activated by salt, the simultaneity explaining the small variation observed in the steady-state reduction level of cytochrome c. A simple kinetic core model is used to show that changes in the rate of dissociation of cytochrome c from the membrane can explain the observed kinetic changes in both cytochrome c reduction and cytochrome c oxidation. The stimulation is proposed to be the result of an increase in the rate constant of cytochrome c dissociation from the membrane induced by cation screening. We conclude that this type of modular kinetic analysis is a powerful tool to identify and quantitatively characterize multiple-site effects on the mitochondrial respiratory chain.
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Affiliation(s)
- K Krab
- Department of Molecular Cell Physiology, BioCentrum Amsterdam, Faculty of Biology, Vrije Universiteit, Amsterdam, The Netherlands.
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26
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Otten MF, Reijnders WN, Bedaux JJ, Westerhoff HV, Krab K, Van Spanning RJ. The reduction state of the Q-pool regulates the electron flux through the branched respiratory network of Paracoccus denitrificans. Eur J Biochem 1999; 261:767-74. [PMID: 10215894 DOI: 10.1046/j.1432-1327.1999.00334.x] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
In this work we demonstrate how the reduction state of the Q-pool determines the distribution of electron flow over the two quinol-oxidising branches in Paracoccus denitrificans: one to quinol oxidase, the other via the cytochrome bc1 complex to the cytochrome c oxidases. The dependence of the electron-flow rate to oxygen on the fraction of quinol in the Q-pool was determined in membrane fractions and in intact cells of the wild-type strain, a bc1-negative mutant and a quinol oxidase-negative mutant. Membrane fractions of the bc1-negative mutant consumed oxygen at significant rates only at much higher extents of Q reduction than did the wild-type strain or the quinol oxidase-negative mutant. In the membrane fractions, dependence on the Q redox state was exceptionally strong corresponding to elasticity coefficients close to 2 or higher. In intact cells, the dependence was weaker. In uncoupled cells the dependence of the oxygen-consumption rates on the fractions of quinol in the Q-pool in the wild-type strain and in the two mutants came closer to that found for the membrane fractions. We also determined the dependence for membrane fractions of the wild-type in the absence and presence of antimycin A, an inhibitor of the bc1 complex. The dependence in the presence of antimycin A resembled that of the bc1-negative mutant. These results indicate that electron-flow distribution between the two quinol-oxidising branches in P. denitrificans is not only determined by regulated gene expression but also, and to a larger extent, by the reduction state of the Q-pool.
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Affiliation(s)
- M F Otten
- Department of Molecular Cell Physiology, Faculty of Biology, BioCentrum Amsterdam, Free University, The Netherlands
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27
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Affourtit C, Albury MS, Krab K, Moore AL. Functional expression of the plant alternative oxidase affects growth of the yeast Schizosaccharomyces pombe. J Biol Chem 1999; 274:6212-8. [PMID: 10037707 DOI: 10.1074/jbc.274.10.6212] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
We have investigated the extent to which functional expression of the plant alternative oxidase (from Sauromatum guttatum) in Schizosaccharomyces pombe affects yeast growth. When cells are cultured on glycerol, the maximum specific growth rate is decreased from 0.13 to 0.11 h-1 while growth yield is lowered by 20% (from 1. 14 x 10(8) to 9.12 x 10(7) cells ml-1). Kinetic studies suggest that the effect on growth is mitochondrial in origin. In isolated mitochondria we found that the alternative oxidase actively competes with the cytochrome pathway for reducing equivalents and contributes up to 24% to the overall respiratory activity. Metabolic control analysis reveals that the alternative oxidase exerts a considerable degree of control (22%) on total electron flux. Furthermore, the negative control exerted by the alternative oxidase on the flux ratio of electrons through the cytochrome and alternative pathways is comparable with the positive control exerted on this flux-ratio by the cytochrome pathway. To our knowledge, this is the first paper to report a phenotypic effect because of plant alternative oxidase expression. We suggest that the effect on growth is the result of high engagement of the non-protonmotive alternative oxidase in yeast respiration that, consequently, lowers the efficiency of energy conservation and hence growth.
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Affiliation(s)
- C Affourtit
- Department of Biochemistry, School of Biological Sciences, University of Sussex, Falmer, Brighton BN1 9QG, United Kingdom
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Affourtit C, Leach GR, Krab K, Moore AL. Kinetic interaction between oxidases and dehydrogenases in plant mitochondria. Biochem Soc Trans 1997; 25:60S. [PMID: 9056958 DOI: 10.1042/bst025060s] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Affiliation(s)
- C Affourtit
- Biochemistry Department, Sussex University, Falmer, Brighton, UK
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29
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Bakels RH, Van Wielink JE, Krab K, Van Walraven HS. The effect of sulfite on the ATP hydrolysis and synthesis activities in chloroplasts and cyanobacterial membrane vesicles can be explained by competition with phosphate. Arch Biochem Biophys 1996; 332:170-4. [PMID: 8806722 DOI: 10.1006/abbi.1996.0329] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
The effect of sulfite on ATP synthesis and hydrolysis activities is investigated in spinach chloroplasts and in membrane vesicles from the cyanobacterium Synechococcus 6716. Sulfite inhibits phenazine methosulfate-mediated cyclic photophosphorylation both in thiol-modulated chloroplasts and in cyanobacterial membranes with HSO3- (bisulfite) as the active ionic species. The observed inhibition is not due to inhibition of electron transfer or to uncoupling by sulfite. ATP synthesis in cyanobacterial membranes is more sensitive to sulfite when the inorganic phosphate concentration is decreased. This indicates competition between sulfite and phosphate for the same binding site on the ATP synthase. In cyanobacterial membranes sulfite can replace a proton gradient as activator of ATP hydrolysis in the same way as in reduced chloroplasts. By modeling, competition between sulfite and phosphate can fully explain the findings concerning both inhibition and activation.
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Affiliation(s)
- R H Bakels
- Department of Physiology and Biochemistry of Plants, BioCentrum Amsterdam, The Netherlands
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30
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Kraayenhof R, Sterk GJ, Wong Fong Sang HW, Krab K, Epand RM. Monovalent cations differentially affect membrane surface properties and membrane curvature, as revealed by fluorescent probes and dynamic light scattering. Biochim Biophys Acta 1996; 1282:293-302. [PMID: 8703985 DOI: 10.1016/0005-2736(96)00069-7] [Citation(s) in RCA: 42] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
The effects of monovalent cations on the interfacial electrostatic potential (psi d), hydrodynamic shear boundary distance (ds), and membrane curvature were studied in large unilamellar phospholipid and galacto/sulfolipid liposomes containing different fractions of negatively charged lipids. The differential effects of alkali metal ions on psi d could be accurately determined at physiological surface charge densities with a surface-anchored fluorescent probe. Li+ and Na+ more effectively decrease psi d and exhibit higher association constants (Kas) than K+ and Cs+. These two groups of cations display qualitatively different perturbations of the interfacial structure. Combining Kas values with the electrokinetic (zeta) potentials yielded the respective ds values. At low ionic strength ds more substantially increases with Li+ or Na+ than with K+ or Cs+. Increasing surface charge density causes increased membrane curvature in the presence of K+ or Cs+, but this is largely prevented by Li+ or Na+. Membrane binding of the amphiphilic cation acridine orange decreases surface charge and membrane curvature more extensively than H3O+, Li+, and Na+. The differential interface-perturbing behavior of monovalent cations is discussed with regard to their different hydration tendencies that will modulate the extent and stability of the hydrogen-bond network along the charged membrane surface.
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Affiliation(s)
- R Kraayenhof
- Institute of Molecular Biological Sciences, BioCentrum Amsterdam, Vrije Universiteit, The Netherlands.
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31
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Leach GR, Krab K, Whitehouse DG, Moore AL. Kinetic analysis of the mitochondrial quinol-oxidizing enzymes during development of thermogenesis in Arum maculatum L. Biochem J 1996; 317 ( Pt 1):313-9. [PMID: 8694781 PMCID: PMC1217480 DOI: 10.1042/bj3170313] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
The dependence of the rate of oxygen uptake upon the ubiquinone (Q)-pool reduction level in mitochondria isolated during the development of thermogenesis of Arum maculatum spadices has been investigated. At the alpha-stage of development, the respiratory rate was linearly dependent upon the reduction level of the Q-pool (Qr) both under state-3 and -4 conditions. Progression through the beta/gamma to the delta-stage resulted in a non-linear dependence of the state-4 rate on Qr. In the delta-stage of development, both state-3 and -4 respiratory rates were linearly dependent upon Qr due to a shift in the engagement of the alternative oxidase to lower levels of Qr. Western blot analysis revealed that increased alternative oxidase activity could be correlated with expression of a 35 kDa protein. Respiratory control was only observed with mitochondria in the alpha-stage of development. At the beta/gamma-stage of development, the addition of ADP resulted in a significant oxidation of the Q-pool which was accompanied by a decrease in the respiratory rate. This was due either to decreased contribution of the alternative pathway to the overall respiratory rate under state 3 or by deactivation of succinate dehydrogenase activity by ADP. Cold-storage of the spadices at the beta-stage of development led to increased activity of both the cytochrome pathway and succinate dehydrogenase, without any change in alternative oxidase activity. Results are discussed in terms of how changes in the activation level of the alternative oxidase and succinate dehydrogenase influence the activity and engagement of the quinol-oxidizing pathways during the development of thermogenesis in A. maculatum.
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Affiliation(s)
- G R Leach
- Biochemistry Department, University of Sussex, Falmer, Brighton, U.K
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32
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de Gier JW, Schepper M, Reijnders WN, van Dyck SJ, Slotboom DJ, Warne A, Saraste M, Krab K, Finel M, Stouthamer AH, van Spanning RJ, van der Oost J. Structural and functional analysis of aa3-type and cbb3-type cytochrome c oxidases of Paracoccus denitrificans reveals significant differences in proton-pump design. Mol Microbiol 1996; 20:1247-60. [PMID: 8809776 DOI: 10.1111/j.1365-2958.1996.tb02644.x] [Citation(s) in RCA: 68] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
In Paracoccus denitrificans the aa3-type cytochrome c oxidase and the bb3-type quinol oxidase have previously been characterized in detail, both biochemically and genetically. Here we report on the isolation of a genomic locus that harbours the gene cluster ccoNOOP, and demonstrate that it encodes an alternative cbb3-type cytochrome c oxidase. This oxidase has previously been shown to be specifically induced at low oxygen tensions, suggesting that its expression is controlled by an oxygen-sensing mechanism. This view is corroborated by the observation that the ccoNOOP gene cluster is preceded by a gene that encodes an FNR homologue and that its promoter region contains an FNR-binding motif. Biochemical and physiological analyses of a set of oxidase mutants revealed that, at least under the conditions tested, cytochromes aa3, bb3 and cbb3 make up the complete set of terminal oxidases in P. denitrificans. Proton-translocation measurements of these oxidase mutants indicate that all three oxidase types have the capacity to pump protons. Previously, however, we have reported decreased H+/e- coupling efficiencies of the cbb3-type oxidase under certain conditions. Sequence alignment suggests that many residues that have been proposed to constitute the chemical and pumped proton channels in cytochrome aa3 (and probably also in cytochrome bb3) are not conserved in cytochrome cbb3. It is concluded that the design of the proton pump in cytochrome cbb3 differs significantly from that in the other oxidase types.
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Affiliation(s)
- J W de Gier
- Department of Molecular and Cellular Biology, BioCentrum Amsterdam, Vrije Universiteit, Netherlands
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33
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Day DA, Krab K, Lambers H, Moore AL, Siedow JN, Wagner AM, Wiskich JT. The Cyanide-Resistant Oxidase: To Inhibit or Not to Inhibit, That Is the Question. Plant Physiol 1996; 110:1-2. [PMID: 12226168 PMCID: PMC157687 DOI: 10.1104/pp.110.1.1] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/18/2023]
Affiliation(s)
- D. A. Day
- Division of Biochemistry and Molecular Biology, Australian National University, Canberra ACT 0200, Australia (D.A.D.)
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Abstract
The kinetic modelling of the respiratory network in plant mitochondria is discussed, with emphasis on the importance of the choice of boundary conditions, and of modelling of both quinol-oxidising and quinone-reducing pathways. This allows quantitative understanding of the interplay between the different pathways, and of the functioning of the plant respiratory network in terms of the kinetic properties of its component parts. The effects of activation of especially succinate dehydrogenase and the cyanide-insensitive alternative oxidase are discussed. Phenomena, such as respiratory control ratios depending on the substrate, shortcomings of the Bahr and Bonner model for electron distribution between the oxidases and reversed respiratory control, are explained. The relation to metabolic control analysis of the respiratory network is discussed in terms of top-down analysis.
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Affiliation(s)
- K Krab
- Department of Molecular and Cellular Biology, Vrije Universiteit, Amsterdam, The Netherlands
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35
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Krab K, van den Bergen CW, Moore AL. A mathematical model to describe quinone pool kinetics and analyse control of respiration in plant mitochondria. Biochem Soc Trans 1995; 23:289S. [PMID: 7672315 DOI: 10.1042/bst023289s] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Affiliation(s)
- K Krab
- Department of Molecular and Cellular Biology, Vrije Universiteit, Amsterdam, The Netherlands
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Van den Bergen CW, Wagner AM, Krab K, Moore AL. The relationship between electron flux and the redox poise of the quinone pool in plant mitochondria. Interplay between quinol-oxidizing and quinone-reducing pathways. Eur J Biochem 1994; 226:1071-8. [PMID: 7813462 DOI: 10.1111/j.1432-1033.1994.01071.x] [Citation(s) in RCA: 64] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
The dependence of electron flux through quinone-reducing and quinol-oxidizing pathways on the redox state of the ubiquinone (Q) pool was investigated in plant mitochondria isolated from potato (Solanum tuberosum cv. Bintje, fresh tissue and callus), sweet potato (Ipomoea batatas) and Arum italicum. We have determined the redox state of the Q pool with two different methods, the Q-electrode and Q-extraction techniques. Although results from the two techniques agree well, in all tissues tested (with the exception of fresh potato) an inactive pool of QH2 was detected by the extraction technique that was not observed with the electrode. In potato callus mitochondria, an inactive Q pool was also found. An advantage of the extraction method is that it permits determination of the Q redox state in the presence of substances that interfere with the Q-electrode, such as benzohydroxamate and NADH. We have studied the relation between rate and Q redox state for both quinol-oxidizing and quinone-reducing pathways under a variety of metabolic conditions including state 3, state 4, in the presence of myxothiazol, and benzohydroxamate. Under state 4 conditions or in the presence of myxothiazol, a non-linear dependence of the rate of respiration on the Q-redox state was observed in potato callus mitochondria and in sweet potato mitochondria. The addition of benzohydroxamate, under state 4 conditions, removed this non-linearity confirming that it is due to activity of the cyanide-resistant pathway. The relation between rate and Q redox state for the external NADH dehydrogenase in potato callus mitochondria was found to differ from that of succinate dehydrogenase. It is suggested that the oxidation of cytoplasmic NADH in vivo uses the cyanide-resistant pathway more than the pathway involving the oxidation of succinate. A model is used to predict the kinetic behaviour of the respiratory network. It is shown that titrations with inhibitors of the alternative oxidase cannot be used to demonstrate a pure overflow function of the alternative oxidase.
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Affiliation(s)
- C W Van den Bergen
- Department of Molecular and Cellular Biology, Vrije Universiteit, Amsterdam, The Netherlands
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Affiliation(s)
- G R Leach
- Biochemistry Department, University of Sussex, Falmer, Brighton, U.K
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Moore AL, Leach G, Whitehouse DG, van den Bergen CW, Wagner AM, Krab K. Control of oxidative phosphorylation in plant mitochondria: The role of non-phosphorylating pathways. Biochimica et Biophysica Acta (BBA) - Bioenergetics 1994. [DOI: 10.1016/0005-2728(94)90101-5] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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Bakels RH, Van Walraven HS, Van Wielink JE, Van Der Zwet-De Graaff I, Krenn BE, Krab K, Berden JA, Kraayenhof R. The effect of sulfite on the ATP hydrolysis and synthesis activity of membrane-bound H(+)-ATP synthase from various species. Biochem Biophys Res Commun 1994; 201:487-92. [PMID: 8002977 DOI: 10.1006/bbrc.1994.1728] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
The action of sulfite on ATP hydrolysis and synthesis activities is investigated in membrane vesicles prepared from the cyanobacterium Synechococcus 6716, chromatophores from the photosynthetic purple bacterium Rhodospirillum rubrum, membrane vesicles from the related non-photosynthetic bacterium Paracoccus denitrificans, and bovine heart submitochondrial particles. Without any further pretreatment ATP hydrolysis is stimulated by sulfite in all four membrane preparations. Typically ATP synthesis in the cyanobacterial membrane vesicles is inhibited by sulfite, whereas ATP synthesis in chromatophores and the submitochondrial particles is not. These differences in sensitivity of ATP synthesis to sulfite, however, correspond well with the distribution of (photosynthetic) sulfur oxidizing pathways in the remaining three organisms/organelles compared in this study.
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Affiliation(s)
- R H Bakels
- Department of Physiology and Biochemistry of Plants, Institute of Molecular Biological Sciences, BioCentrum Amsterdam, The Netherlands
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Bakels RH, van Walraven HS, Krab K, Scholts MJ, Kraayenhof R. On the activation mechanism of the H(+)-ATP synthase and unusual thermodynamic properties in the alkalophilic cyanobacterium Spirulina platensis. Eur J Biochem 1993; 213:957-64. [PMID: 8504834 DOI: 10.1111/j.1432-1033.1993.tb17840.x] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
The activation requirements and thermodynamic characteristics of ATP synthase from the alkalophilic cyanobacterium Spirulina platensis were studied in coupled membrane vesicles. Activation by methanol increased the Vmax, while the Km for MgATP was unaffected (0.7 mM). We propose that in Sp. platensis, as in chloroplasts, the activating effect of methanol is based on perturbation of the gamma-epsilon subunit interaction. Light-driven ATP synthesis by membrane vesicles of Sp. platensis was stimulated by dithiothreitol. The characteristics of the activation of the ATP synthase by the proton electrochemical potential difference (delta mu H+) were analyzed on the basis of the uncoupled rates of ATP hydrolysis as a function of a previously applied proton gradient. Two values of delta mu H+, at which 50% of the enzyme is active, were found; 13-14 kJ.mol-1 for untreated membrane vesicles, and 4-8 kJ.mol-1 for light-treated and dithiothreitol-treated membrane vesicles. These values are lower than the corresponding values for the oxidized and reduced forms, respectively, of the chloroplast enzyme. Although no bulk proton gradient could be observed, membrane vesicles of Sp. platensis were able to maintain an equilibrium phosphate potential (delta Gp) of 40-43.5 kJ.mol-1, comparable to values found for Synechococcus 6716 and Anabaena 7120 membrane vesicles. Acid/base-transition experiments showed that the thermodynamic threshold, delta mu H+, for ATP synthesis, catalyzed by light-treated and dithiothreitol-treated Spirulina membrane vesicles, was less than 5 kJ.mol-1. The activation characteristics and the low thermodynamic threshold allow ATP synthesis to occur at low delta mu H+ values. The findings are discussed, both with respect to differences and similarities with the enzymes from chloroplasts and other cyanobacteria, and with respect to the alkalophilic properties of Sp. platensis.
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Affiliation(s)
- R H Bakels
- Department of Molecular and Cellular Biology, Vrije Universiteit, Amsterdam, The Netherlands
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Wagner AM, van den Bergen CW, Krab K. Modulation of the Access of Exogenous NAD(P)H to the Alternative Pathway in Potato Tuber Callus Mitochondria with Triton X-100. Plant Physiol 1992; 100:1259-62. [PMID: 16653114 PMCID: PMC1075775 DOI: 10.1104/pp.100.3.1259] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/08/2023]
Abstract
Alternative oxidase activity in potato tuber (Solanum tuberosum L. cv Bintje) callus mitochondria with exogenous NAD(P)H as substrate is inhibited by low concentrations of the detergent Triton X-100. Alternative oxidase activity with succinate or malate as substrate is not affected by these low concentrations of Triton X-100. Cytochrome pathway activity was not influenced under these conditions, neither with endogenous nor with exogenous substrate. Washing of Triton X-100-treated mitochondria did partially restore both uninhibited and CN-resistant NADH oxidation, indicating that under these conditions Triton X-100 does not permanently remove major components from the mitochondrial membrane. Apparently, it is possible to manipulate mitochondria in such a way that the access of exogenous NADH to the alternative pathway is blocked while access to the cytochrome pathway is uninhibited. It is suggested that membrane conditions have a regulatory function (possibly via influencing the diffusion path) in the oxidation of exogenous NADH via the alternative pathway.
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Affiliation(s)
- A M Wagner
- Department of Physiology and Biochemistry of Plants, Vrije Universiteit, De Boelelaan 1087, 1081 HV Amsterdam, The Netherlands
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Krab K, van Wezel J. Improved derivation of phosphate potentials at different temperatures. Biochimica et Biophysica Acta (BBA) - Bioenergetics 1992. [DOI: 10.1016/s0005-2728(05)80333-0] [Citation(s) in RCA: 24] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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van der Oost J, Bulthuis BA, Feitz S, Krab K, Kraayenhof R. Fermentation metabolism of the unicellular cyanobacterium Cyanothece PCC 7822. Arch Microbiol 1989. [DOI: 10.1007/bf00446921] [Citation(s) in RCA: 53] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
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de Wolf F, Krab K, Visschers R, de Waard J, Kraayenhof R. Studies on well-coupled Photosystem I-enriched subchloroplast vesicles — characteristics and reinterpretation of single-turnover cyclic electron transfer. Biochimica et Biophysica Acta (BBA) - Bioenergetics 1988. [DOI: 10.1016/0005-2728(88)90026-6] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
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Krab K, Wikström M. Principles of coupling between electron transfer and proton translocation with special reference to proton-translocation mechanisms in cytochrome oxidase. Biochim Biophys Acta 1987; 895:25-39. [PMID: 2449910 DOI: 10.1016/s0304-4173(87)80015-0] [Citation(s) in RCA: 52] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
The recent general acceptance of the proton-pumping function of cytochrome oxidase has stimulated discussion and experiment on possible underlying molecular mechanisms. Adequate experimental design requires clear understanding of the theoretical principles governing such a linked function. The increasing structural knowledge of cytochrome oxidase also contributes to a present-day requirement of more precise chemical and physical description of redox-linked proton translocation, which is the fundamental process underlying conservation of energy from aerobic metabolism in all eukaryotes and many bacteria. This essay is based on our original theoretical treatment of this problem, which is expanded here to include discussion of more recent analyses by others, classification of different types of coupling principles, as well as some concrete proposed molecular mechanisms. The latter will be analysed qualitatively, and in some cases quantitatively where this is possible, using a common theoretical framework to help comparison between models. Experimental findings relevant to this problem will be critically reviewed, and some suggestions will be made to stimulate further experiments dedicated to clarify the problem.
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Affiliation(s)
- K Krab
- Department of Medical Chemistry, University of Helsinki, Finland
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Kraayenhof R, De Wolf F, Van Walraven H, Krab K. The significance of interfacial charge and proton displacements for the mechanism of energy transduction in biomembranes. ACTA ACUST UNITED AC 1986. [DOI: 10.1016/0302-4598(86)85007-3] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
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de Wolf F, Galmiche J, Krab K, Kraayenhof R, Girault G. Studies on well-coupled Photosystem-I-enriched subchloroplast vesicles. Kinetic aspects of flash-induced energy transduction. Biochimica et Biophysica Acta (BBA) - Bioenergetics 1986. [DOI: 10.1016/0005-2728(86)90137-4] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
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Van Walraven H, Van Der Bend R, Hagendoorn M, Haak N, Oskam A, Oostdam A, Krab K, Kraayenhof R. Comparison of ATP synthesis efficiencies in ATPase proteoliposomes of different complexities. ACTA ACUST UNITED AC 1986. [DOI: 10.1016/0302-4598(86)80055-1] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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Krab K, Wikström M. Determination of the stoichiometry of redox-linked proton translocation from the kinetics of pulse experiments. A simulation study. FEBS Lett 1986; 201:198-204. [PMID: 3011510 DOI: 10.1016/0014-5793(86)80608-1] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
We have previously published a simple kinetic model to analyse possible pitfalls in kinetic measurements of H+/O ratios in mitochondria [(1984) FEBS Lett. 178, 187-192]. While this model demonstrated how relative electrode response times may affect the results, it did not adequately describe the kinetics of proton back-diffusion across the membrane. Here this model is further developed and improved, and shown to give a good quantitative description of both oxygen-pulse type experiments as well as of experiments where the reaction is started by photolysis of the cytochrome c oxidase-CO complex. Simulations based on this model reveal that the extrapolation procedure used by Lehninger et al. [e.g. (1984) J. Biol. Chem. 259, 4802-4811] to estimate the H+/O ratio will tend to yield overestimated values. This is mainly due to the back-diffusion of protons into the mitochondria, which is not correctly accounted for by this extrapolation.
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