DOCSLIB.ORG

Redox Potential of the Terminal Quinone Electron Acceptor QB in Photosystem II Reveals the Mechanism of Electron Transfer Regulation

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Redox Potential of the Terminal Quinone Electron Acceptor QB in Photosystem II Reveals the Mechanism of Electron Transfer Regulation Redox potential of the terminal quinone electron acceptor QB in photosystem II reveals the mechanism of electron transfer regulation Yuki Kato1, Ryo Nagao, and Takumi Noguchi1 Division of Material Science, Graduate School of Science, Nagoya University, Nagoya 464-8602, Japan Edited by Pierre A. Joliot, Institut de Biologie Physico-Chimique, Paris, France, and approved December 4, 2015 (received for review October 12, 2015) Photosystem II (PSII) extracts electrons from water at a Mn4CaO5 (Em values). Both forward and backward electron transfers are cluster using light energy and then transfers them to two plas- important; backward electron transfers control charge recombina- toquinones, the primary quinone electron acceptor QA and the tion in PSII, and this serves as photoprotection for PSII proteins secondary quinone electron acceptor QB. This forward electron (5, 14–17). PSII involves specific mechanisms to regulate for- transfer is an essential process in light energy conversion. Mean- ward and backward electron transfer reactions in response to while, backward electron transfer is also significant in photopro- environmental changes. For instance, in strong light, some spe- tection of PSII proteins. Modulation of the redox potential (Em) gap cies of cyanobacteria increase the Em of Pheo to facilitate charge of QA and QB mainly regulates the forward and backward electron recombination. Specifically, they exchange D1 subunits origi- transfers in PSII. However, the full scheme of electron transfer nating from different psbA genes to change the hydrogen bond regulation remains unresolved due to the unknown Em value of interactions of Pheo (16–20). On the other hand, it was found QB. Here, for the first time (to our knowledge), the Em value of QB that impairment of the Mn4CaO5 cluster led to a significant in- reduction was measured directly using spectroelectrochemistry in crease in the Em of QA by ∼150 mV (21–27). This potential in- combination with light-induced Fourier transform infrared differ- crease was thought to inhibit forward electron transfer to QB to − − ence spectroscopy. The Em(QB /QB) was determined to be approx- promote direct relaxation of QA without forming triplet-state imately +90 mV and was virtually unaffected by depletion of the Chl, a precursor of harmful singlet oxygen (2, 5, 14, 15, 17, 23). BIOPHYSICS AND Mn CaO cluster. This insensitivity of E (Q −/Q ), in combination − + 4 5 m B B In addition, charge recombination of QA with P680 prevents COMPUTATIONAL BIOLOGY − + with the known large upshift of Em(QA /QA), explains the mecha- oxidative damage by high-potential P680 (5). However, the full nism of PSII photoprotection with an impaired Mn4CaO5 cluster, in mechanism of photoprotection by the regulation of the quinone which a large decrease in the Em gap between QA and QB pro- electron acceptor E values remains to be resolved, because the − m motes rapid charge recombination via QA . Em of QB has not been determined conclusively, and the effect of Mn4CaO5 cluster inactivation on it has not been examined (5). photosynthesis | spectroelectrochemistry | FTIR Although the Em of the single reduction of QB has been es- timated to be ∼80 mV higher than that of QA from kinetic and n oxygenic photosynthesis in plants and cyanobacteria, photo- thermodynamic data (28–32), so far no reports have measured Isystem II (PSII) has an important function in light-driven water the Em of QB directly. In contrast, the Em of QA was measured oxidation, a process that leads to the generation of electrons and extensively using chemical or electrochemical titrations and de- protons for CO reduction and ATP synthesis, respectively (1–3). termined to be approximately −100 mV for oxygen-evolving PSII 2 – Photosynthetic water oxidation also produces molecular oxygen (21 27). The main reason for this difference is due to the fact that the QA reaction can be monitored readily by fluorescence mea- as a byproduct, which is the source of atmospheric oxygen and − sustains virtually all life on Earth. PSII reactions are initiated by surement in that an increase in fluorescence indicates QA formation light-induced charge separation between a chlorophyll (Chl) di- mer (P680) and a pheophytin (Pheo) electron acceptor, leading Significance + − to the formation of a P680 Pheo radical pair (4, 5). An electron + hole on P680 is transferred to a Mn4CaO5 cluster, the catalytic In photosynthesis, photosystem II (PSII) has a function of ab- center of water oxidation, via the redox-active tyrosine, YZ (D1- stracting electrons from water using light energy and trans- Tyr161). At the Mn4CaO5 cluster, water oxidation proceeds ferring them to a quinone molecule. In addition to the forward through a cycle of five intermediates denoted Sn states (n = 0–4) electron transfer in PSII, which is essential in energy conversion, (6, 7). On the electron acceptor side, the electron is transferred backward electron transfer is important in photoprotection of − PSII proteins. Forward and backward electron transfers in PSII are from Pheo to the primary quinone electron acceptor QA and regulated by the redox potential (E ) gap of quinone electron then to the secondary quinone electron acceptor QB (8, 9). QA m acceptors, Q and Q . However, the regulation mechanism is still and QB have many similarities: they consist of plastoquinone A B (PQ), are located symmetrically around a nonheme iron center, unclear because Em of QB has not been determined. We directly and interact with D2 and D1 proteins, respectively, in a similar measured Em of QB using an electrochemical method in combi- manner (Fig. 1) (10, 11). However, they play significantly dif- nation with Fourier transform infrared spectroscopy. Our results ferent roles in PSII (8, 9). Q is only singly reduced to transfer an clearly explain the mechanism of electron transfer regulation in A PSII relevant to photoprotection. electron to QB, whereas QB accepts one or two electrons. When − Q is doubly reduced, the resultant Q 2 takes up two protons to B B Author contributions: Y.K. and T.N. designed research; Y.K. and R.N. performed research; form plastoquinol (PQH2), which is then released into thylakoid Y.K. and T.N. analyzed data; and Y.K. and T.N. wrote the paper. membranes. Differences between QA and QB could be caused by The authors declare no conflict of interest. differences in the molecular interactions of PQ with surrounding This article is a PNAS Direct Submission. proteins in QA and QB pockets, although the detailed mechanism 1To whom correspondence may be addressed. Email: [email protected] remains to be clarified (12, 13). or [email protected]. Electron transfer reactions in PSII are highly regulated by the This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10. spatial localization of redox components and their redox potentials 1073/pnas.1520211113/-/DCSupplemental. www.pnas.org/cgi/doi/10.1073/pnas.1520211113 PNAS Early Edition | 1of6 Downloaded by guest on October 2, 2021 In this study, we directly measured the Em of QB in PSII using spectroelectrochemistry and light-induced FTIR difference spectroscopy. The effect of Mn4CaO5 cluster depletion on the Em value was also examined. Spectroelectrochemistry has been used to accurately measure the Em values of cofactors in various redox proteins (47, 48) including redox cofactors in PSII (24, 25, 49, 50). FTIR spectroelectrochemistry, which has the additional merit of being able to provide structural information, has also been used to investigate redox reactions of biomolecules and proteins (48, 50–54). This method was recently applied to the nonheme iron center of PSII to examine the effect of Mn de- pletion on the Em value and obtain structural information around the nonheme iron (50). The results in our study showed − that the Em of the first reduction of QB [Em(QB /QB)] was much higher than previously estimated, and the Em of the second re- − duction [Em(PQH2/QB )] was higher than the first reduction. Furthermore, we showed that Mn depletion hardly affected the Em values of QB, in contrast to the large change in the Em of QA (21–27). With these results, the mechanism of photoprotection of PSII when the Mn4CaO5 cluster is inactivated is now clearly explained. Results FTIR difference spectra of PSII core complexes from a ther- mophilic cyanobacterium Thermosynechococcus elongatus upon illumination of a single saturating flash were measured at a series of electrode potentials ranging from +250 to +50 mV (Fig. 2A). At the highest potential of +250 mV, a prominent peak was − observed at 1,480 cm 1, which is typical of the CO/CC stretching − vibration of a QB semiquinone anion (46), whereas at the lowest potential of +50 mV, a similar peak was found at a slightly lower −1 − frequency of 1,478 cm , which is typical of QA (55, 56). A significant change was observed in the ester C=O region (1,750– − − 1,700 cm 1): the intensity of a positive peak at 1,745 cm 1 de- − creased gradually, and a peak at 1,721 cm 1 increased, as the potential was lowered from +250 to +50 mV. The former and − latter peaks were shown previously to belong to QB /QB and − QA /QA differences, respectively, and were proposed to be good markers for discriminating between QB and QA reactions (46). Each peak was assigned to the 132-ester C=O vibration of the nearby Pheo (PheoD2 and PheoD1 for QB and QA, respectively; Fig. 1), which is electrostatically and/or structurally coupled to QB(A) and hence affected by its photoreduction (46). The fre- Fig. 1. Redox cofactors in PSII and the electron transfer pathway (blue ar- −1 rows). For the PSII structure, the X-ray crystallographic structure at 1.9-Å quency difference between 1,745 and 1,721 cm is attributed to resolution (Protein Data Bank ID code 3ARC) (9) was used.
Load more

Recommended publications
  • The Electron Transport Chain in Anaerobically Functioning Eukaryotes
    rl BIOCHIMICA ET BIOPHYSICA ACTA II BBt ELSEVIER Biochimica et Biophysica Acta, 1365 (1998) 71-78 The electron transport chain in anaerobically functioning eukaryotes Aloysius G.M. Tielens*, Jaap J. Van Hellemond Laboratory of Veterinary Biochemistry and Institute for Biomembranes, Utrecht University, P.O. Box 80176, 3508 TD Utrecht, The Netherlands Received 27 January 1998; received in revised form 26 February 1998; accepted 2 March 1998 Abstract Many lower eukaryotes can survive anaerobic conditions via a fermentation pathway that involves the use of the reduction of endogenously produced fumarate as electron sink. This fumarate reduction is linked to electron transport in an especially adapted, anaerobically functioning electron-transport chain. An aerobic energy metabolism with Krebs cycle activity is accompanied by electron transfer from succinate to ubiquinone via complex II of the respiratory chain. On the other hand, in an anaerobic metabolism, where fumarate functions as terminal electron acceptor, electrons are transferred from rhodoquinone to fumarate, which is the reversed direction. Ubiquinone cannot replace rhodoquinone in the process of fumarate reduction in vivo, as ubiquinone can only accept electrons from complex II and cannot donate them to fumarate. Rhodoquinone, with its lower redox potential than ubiquinone, is capable of donating electrons to fumarate. Eukaryotic fumarate reductases were shown to interact with rhodoquinone (a benzoquinone), whereas most prokaryotic fumarate reductases interact with the naphtoquinones mena- quinone and demethylmenaquinone. Fumarate reductase, the enzyme essential for the anaerobic functioning of many eukaryotes, is structurally very similar to succinate dehydrogenase, the Krebs cycle enzyme catalysing the reverse reaction. In prokaryotes these enzymes are differentially expressed depending on the external conditions.
    [Show full text]
  • Biol 1020: Photosynthesis
    Chapter 10: Photosynthesis Energy and Carbon Sources Electromagnetic Spectrum and Light Chloroplasts Photosynthesis Overview Light Reactions C3 Cycle Photorespiration Supplemental Carbon Fixation: C4 and CAM pathways . • List and differentiate the 4 possible groups of organisms based on how they obtain energy and useful carbon. Classification by Energy and Carbon Sources energy source chemotrophs can only get energy directly from chemical compounds phototrophs can get energy directly from light (these organisms can use chemical compounds as energy sources as well) . Classification by Energy and Carbon Sources carbon source autotrophs can fix carbon dioxide, thus they can use CO2 as a carbon source heterotrophs cannot fix CO2; they use organic molecules from other organisms as a carbon source . Classification by Energy and Carbon Sources combined, these leads to 4 possible groups: photoautotrophs – carry out photosynthesis use light energy to fix CO2 store energy in chemical bonds of organic molecules includes green plants, algae, and some bacteria photoheterotrophs – use light energy but cannot fix CO2; some nonsulfur purple bacteria chemoautotrophs – obtain energy from reduced inorganic molecules and use some of it to fix CO2; some bacteria chemoheterotrophs – use organic molecules as both carbon and energy sources dependent completely on other organisms for energy capture and carbon fixation includes all animals, all fungi, most protists, and most bacteria . • List and differentiate the 4 possible groups of
    [Show full text]
  • Donor/Acceptor Electronic Coupling Is a Dynamical Variable Edward W
    Claremont Colleges Scholarship @ Claremont All HMC Faculty Publications and Research HMC Faculty Scholarship 1-1-2000 Solvent as Electron Donor: Donor/Acceptor Electronic Coupling Is a Dynamical Variable Edward W. Castner Jr. Rutgers University Darcy Kennedy '00 Claremont McKenna College Robert J. Cave Harvey Mudd College Recommended Citation Castner, E.W. Jr.; Kennedy, D.; Cave, R.J. “Solvent as Electron Donor: Donor/Acceptor Coupling is a Dynamical Variable,” J. Phys. Chem. A 2000, 104, 2869. DOI: 10.1021/jp9936852 This Article is brought to you for free and open access by the HMC Faculty Scholarship at Scholarship @ Claremont. It has been accepted for inclusion in All HMC Faculty Publications and Research by an authorized administrator of Scholarship @ Claremont. For more information, please contact [email protected]. J. Phys. Chem. A 2000, 104, 2869-2885 2869 ARTICLES Solvent as Electron Donor: Donor/Acceptor Electronic Coupling Is a Dynamical Variable Edward W. Castner, Jr.*,† BrookhaVen National Laboratory, Chemistry Department, Building 555A, Upton, New York 11973-5000 Darcy Kennedy and Robert J. Cave*,‡ HarVey Mudd College, Department of Chemistry, Claremont, California 91711 ReceiVed: October 14, 1999; In Final Form: December 24, 1999 We combine analysis of measurements by femtosecond optical spectroscopy, computer simulations, and the generalized Mulliken-Hush (GMH) theory in the study of electron-transfer reactions and electron donor- acceptor interactions. Our focus is on ultrafast photoinduced electron-transfer reactions from aromatic amine solvent donors to excited-state acceptors. The experimental results from femtosecond dynamical measurements fall into three categories: six coumarin acceptors reductively quenched by N,N-dimethylaniline (DMA), eight electron-donating amine solvents reductively quenching coumarin 152 (7-(dimethylamino)-4-(trifluoromethyl)- coumarin), and reductive quenching dynamics of two coumarins by DMA as a function of dilution in the nonreactive solvents toluene and chlorobenzene.
    [Show full text]
  • Electron Donor-Acceptor Properties of 10(S)-Chlorophyll a Paavo H
    Electron Donor-Acceptor Properties of 10(S)-Chlorophyll a Paavo H. Hynninen Department of Biochemistry. University of Kuopio, P. O. Box 138, SF-70101 Kuopio 10, Finland Z. Naturforsch. 39b, 675 — 678 (1984); received July 12, 1983 Chlorophyll Epimers, Chlorophyll Organization, Stereochemistry, Photosynthesis, Infrared Spectra, Absorption Spectra Evidence for the self-aggregation of 10(S)-chlorophyll a (= chlorophyll a') in nonpolar solvents has been obtained by means of absorption spectroscopy in the visible and infrared regions. The visible absorption spectrum of chlorophyll a' exhibits a shoulder at 680 nm in aliphatic hydrocar­ bon solvents and the infrared spectrum measured in carbon tetrachloride contains an “aggrega­ tion peak” at 1650 cm"1. IR spectroscopy shows, in addition, that the C-10 epimers of chlorophyll a are both present as monomers in tetrahydrofuran. However, in the presence of a small amount of aliphatic alcohol or water, the IR spectrum in tetrahydrofuran at lowered temperatures exhibits an intense, wide absorption band at ~ 1650 cm -1 which was interpreted as arising from the hydrogen bonding of the hydroxyl group to the C-9 keto carbonyl of the chlorophyll. Introduction nesium of another Chi molecule. This results in the The electron donor-acceptor or coordination prop­ formation of dimers and oligomers, (Chl)„. On the erties of chlorophyll (Chi) molecules are of particular basis of the similarities between the electronic ab­ interest in relation to the organization and function sorption spectrum of the in vivo chlorophyll and that of these molecules in photosynthetic membranes of the in vitro prepared oligomeric chlorophyll, it has [1 — 5]. According to the structural formula usually been suggested that the “antenna chlorophyll” con­ written for Chi a (1), the coordination number of the sists of chlorophyll oligomers [2—4].
    [Show full text]
  • Ocean Life, Bioenergetics and Metabolism
    Ocean life, bioenergetics and metabolism Biological Oceanography (OCN 621) Matthew Church (MSB 612) Ecosystems are hierarchically organized • Atoms → Molecules → Cells → Organisms→ Populations→ Communities • This organizational system dictates the pathways that energy and material travel through a system. • Cells are the lowest level of structure capable of performing ALL the functions of life. Classification of life Two primary cellular forms • Prokaryotes: lack internal membrane-bound organelles. Genetic information is not separated from other cell functions. Bacteria and Archaea are prokaryotes. Note however this does not imply these divisions of life are closely related. • Eukaryotes: membrane-bound organelles (nucleus, mitochrondrion, etc .). Compartmentalization (organization) of different cellular functions allows sequential intracellular activities In the ocean, microscopic organisms account for >50% of the living biomass. Controls on types of organisms, abundances, distributions • Habitat: The physical/chemical setting or characteristics of a particular environment, e.g., light vs. dark, cold vs. warm, high vs. low pressure • Each marine habitat supports a somewhat predictable assemblage of organisms that collectively make up the community, e.g., rocky intertidal community, coral reef community, abyssobenthic community • The structure and function of the individuals/populations in these communities arise from evolution and selective adaptations in response to the habitat characteristics • Niche: The role of a particular organism in an integrated community •The ocean is not homogenous: spatial and temporal variability in habitats Clearly distinguishable ocean habitats with elevated “plant” biomass in regions where nutrients are elevated The ocean is stirred more than mixed Sea Surface Temperature Chl a (°C) (mg m-3) Spatial discontinuities at various scales (basin, mesoscale, microscale) in ocean habitats play important roles in controlling plankton growth and distributions.
    [Show full text]
  • Anaerobic Respiration - Advanced
    Chapter 1. Anaerobic Respiration - Advanced CHAPTER 1 Anaerobic Respiration - Advanced Learning Objectives • Distinguish between obligate aerobes, obligate anaerobes, and facultative anaerobes. • Explain that, in the absence of oxygen fermentation reactions must regenerate NAD+ in order for glycolysis to continue making ATP. • Discuss how your muscles continue to work for you even when your respiratory and cardiovascular system can no longer keep up a continuous supply of oxygen. Why does a bakery smell so good? When bread bakes, yeast releases carbon dioxide gas, forming the small holes in bread. The gas was produced by alcoholic fermentation carried out by yeast. Anaerobic Respiration After the photosynthetic “oxygen catastrophe” challenged life between 2.5 and 3 billion years ago, evolution re- bounded with biochemical pathways to harness and protect against oxygen’s power. Today, most organisms use O2 in aerobic respiration to produce ATP. Almost all animals, most fungi, and some bacteria are obligate aerobes, which require oxygen. Some plants and fungi and many bacteria retain the ability to make ATP without oxygen. Recall that O2 is the final electron acceptor at the end of the electron transport chain during aerobic respiration. Oxygen is required for oxidative phosphorylation to produce ATP. But in the absence of O2. ATP must still be made. The facultative anaerobes use ancient anaerobic pathways when oxygen is limited. A few bacteria remain as obligate anaerobes, which die in the presence of oxygen and depend on only the first (anaerobic) stage of cellular respiration. Aerobic and anaerobic pathways diverge after glycolysis splits glucose into two molecules of pyruvate: + C6H12O6 + 2NAD + 2Pi + 2ADP → 2NADH + 2ATP 1 www.ck12.org FIGURE 1.1 Anaerobic and aerobic respiration share the glycolysis pathway.
    [Show full text]
  • PS1 PS2 Stroma H H H H H H H H H
    MIT Department of Biology 7.014 Introductory Biology, Spring 2005 Recitation Section 5 February 16-17, 2005 Biochemistry—Photosynthesis and Respiration A. Photosynthesis background 1. Why do we consider O2 a booster of evolution? The organisms doing only glycolysis were slow and small. The net gain of 2ATP molecules from a molecule of glucose is not enough to fuel more complicated organisms that populate the biosphere today. For that, photosynthesis and respiration needed to develop. The waste product of non-cyclic photosynthesis is O2, and its presence allowed respiration to develop, since O2 could be used as an electron acceptor. 2. Why was it advantageous for a cell to develop photosynthesis? When abiotic sources of energy started to decline, it became advantageous to have the ability to make ATP. While glycolysis allows an organism to make ATP, it requires a source of organic carbon. Developing photosynthesis allowed an organism to become an autotroph—make everything it needs from CO2, NH3, PO4, H2O. Thus, in the environment low in abiotic sources of energy and carbohydrates photosynthetic organisms have selective advantage. 3. Photosynethesis has two phases—light and dark. What does each phase accomplish? The light phase is so named because it is dependent on the presence of light to drive its reactions. Light phase reactions use the energy of the excited chlorophylls to make ATP and NADPH, while producing O2 as a waste product. The dark phase is so named because it is independent from the presence of light. Dark phase is also known as a biosynthetic phase—the phase in which atmospheric CO2 is fixed into organic carbon.
    [Show full text]
  • Influence of Electron Acceptor and Electron Donor on The
    FULL PAPER Carbon Dots www.afm-journal.de Influence of Electron Acceptor and Electron Donor on the Photophysical Properties of Carbon Dots: A Comparative Investigation at the Bulk-State and Single-Particle Level Indrajit Srivastava, John S. Khamo, Subhendu Pandit, Parinaz Fathi, Xuedong Huang, Anleen Cao, Richard T. Haasch, Shuming Nie, Kai Zhang,* and Dipanjan Pan* photocatalysis, photovoltaic applications, Carbon dots (CDs) are extensively studied to investigate their unique optical and bioimaging.[1–15] These nanodots have properties such as undergoing electron transfer in different scenarios. This a multitude of intriguing advantages, work presents an in-depth investigation to study the ensemble-averaged such as their water solubility, low toxicity, state/bulk state and single-particle level photophysical properties of CDs high biocompatibility, easy synthesis tech- niques, and complementary energy and that are passivated with electron-accepting (CD-A) and electron-donating charge transfer properties.[16–25] However, molecules (CD-D) on their surface. The bulk-state experiments reveal that in a despite considerable efforts, many ques- mixture of these CDs, CD-A dominates the overall photophyiscal properties and tions remain about the intrinsic mecha- eventually leads to formation of at least two associated geometries, which is nisms governing their photoluminescence dependent on time, concentration, intramolecular electron/charge transfer, and (PL) and its subsequent capability to par- ticipate in photoinduced charge-transfer hydrogen bonding. Single-particle studies, however, do not reveal an “acceptor- processes.[26,27] dominating” scenario based on analysis of instantaneous intensity, bleaching For charge-transfer processes, having kinetics, and photoblinking, indicating that the direct interaction of these CDs a precise control over the interactions may affect their photophysical properties in the bulk state due to formation of between the two components is of hierarchical structural assemblies.
    [Show full text]
  • Electron Donor and Acceptor Utilization by Halorespiring Bacteria'
    Electron donor andaccepto r utilizationb y halorespiring bacteria Maurice L.G.C. Luijten CENTRALS LANDBOUWCATALOGUS 0000 0950 9080 Promotoren Prof.dr .W.M . de Vos Hoogleraar ind eMicrobiologi c Wageningen Universiteit Prof.dr .ir .A.J.M .Stam s Persoonlijk hoogleraar bij hetlaboratoriu mvoo r Microbiologic Laboratorium voor Microbiologic, Wageningen Universiteit Copromotoren Dr.G .Schra a Universitair docent Laboratorium voor Microbiologic, Wageningen Universiteit Dr.A.A.M . Langenhoff Senior researcher/project leader Milieubiotechnologie, TNO-MEP Promotiecommissie Prof. E.J.Bouwe r John's Hopkins University, Baltimore, USA Prof.dr .C .Hollige r EPFL, Lausanne, Switzerland Dr.F .Volkerin g Tauw bv, Deventer, Nederland Prof. dr.ir .W.H . Rulkens Wageningen Universteit Dit onderzoek is uitgevoerd binnen de onderzoekschool SENSE (Netherlands Research School forth e Socio-Economic andNatura l Sciences ofth e Environment). LV''-:- v. •:-:::'.Ifir Electron donor and acceptor utilizationb y halorespiring bacteria Maurice L.G.C.Luijte n Proefschrift Terverkrijgin g van de graadva n doctor opgeza gva n derecto r magnificus van Wageningen Universiteit, prof. dr. ir. L. Speelman, inhe t openbaar te verdedigen opvrijda g 11 juni 2004 desnamiddag s te half twee in deAula . \ '\ i ocXi ^ Electron donor and acceptor utilization byhalorespirin g bacteria Maurice L.G.C. Luijten Ph.D.thesi sWageninge n University, Wageningen, The Netherlands 2004 ISBN 90-5804-067-1 Front cover: Modified EMpictur e ofSulfurospirillum halorespirans PCE-M2 — ry ' Stellingen 1.El k nadeel heb zijn voordeel. Dit proefschrift. 2. De ene volledige reductie van PCE is de andere nog niet. Dit proefschrift. 3. Sectorale communicatie reikt niet ver genoeg. HRH the Prince of Orange, Wat.
    [Show full text]
  • Redox Reactions Is
    Chapter 10 OXIDATION-REDUCTION REACTIONS Oxidation – reduction reactions are those involving the transfer of electrons from one substance to another (no bonding formed or broken). Example: Fe 3+ + e- çè Fe 2+ Protons (H+) are often involved in these reactions also. Another example of redox reactions is: - + H2O2 + 2e + 2H 2H2O Rules for the assigning of oxidation numbers 1. All species in their elemental form are given the oxidatio435n number of zero. 2. All monoatomic ions have the same oxidation number as the charge on the ion. e.g. Mg 2+ has the oxidation number of +2. 3. All combined hydrogen has an oxidation number of +1 (except metal hydrides where its oxidation number is -1). 4. All combined oxygen has an oxidation number of -2 (except peroxides where the oxidation number is -1). 5. In polyatomic species, the sum of the oxidation numbers of the element in the ion equals the charge on that species (we can use this to find the oxidation number of elements in polyatomic species). A. Source of electrons in soils. Electrons dTPSSo not flow around by themselves but they m ust be provided by some sources . In soils, the main source of electrons is carbon atoms of organic matter because carbon has a wide range of oxidation states. Example: CH4 + 2O2 2H2O + CO2 Ox. # (-4) Ox. # (+4) - The reaction (CH4 ® CO2) releases 8e Other common sources of e – are nitrogen and sulfur atoms because they can also have several oxidation states. The availability of electrons usually controls the oxidation/reduction reactions and this availability is expressed as redox potentials.
    [Show full text]
  • Module 3 Microbial Metabolism
    Module 3 Microbial Metabolism © 2013 Pearson Education, Inc. Chapter 5 Microbial Metabolism © 2013 Pearson Education, Inc. Lectures prepared by Helmut Kae Lectures prepared by Christine L. Case Copyright © 2013 Pearson Education, Inc. Catabolic and Anabolic Reactions § Metabolism: the sum of the chemical reactions in an organism § Two general types of metabolic reactions § Catabolism: provides energy and building blocks for anabolism § Anabolism: uses energy and building blocks to build large molecules § Recall from Chapter 2 § Energy can be stored when covalent bonds form § Energy can be released when covalent bonds broken © 2013 Pearson Education, Inc. Catabolic Reactions § Breakdown of complex substances to small molecules § Degradative reactions § Breaking of covalent bonds § What type of reaction used to break covalent bonds? § Purpose is to generate energy, make building blocks § Releases energy stored in bonds § Breakdown products used to build new molecules § Eg, breakdown of glucose for energy © 2013 Pearson Education, Inc. Anabolic Reactions § Building macromolecules from small molecules § Biosynthetic reactions § Forming of covalent bonds § What type of reaction used to form covalent bonds? § Requires energy to form bonds § Purpose is to generate materials for cell growth § Eg, making proteins from amino acids © 2013 Pearson Education, Inc. Figure 5.1 The role of ATP in coupling anabolic and catabolic reactions. Catabolism releases energy by oxidation of molecules Energy is Energy is released by stored in hydrolysis molecules of ATP of ATP Anabolism uses energy to synthesize macromolecules that make up the cell © 2013 Pearson Education, Inc. Catabolic and Anabolic Reactions § A metabolic pathway is a sequence of chemical reactions in a cell § Metabolic pathways are controlled by enzymes © 2013 Pearson Education, Inc.
    [Show full text]
  • Glossary - Botany Plant Physiology
    1 Glossary - Botany Plant Physiology Abscission: The dropping off of leaves, flowers, fruits, or other plant parts, usually following the formation of an abscission zone. A. Zone: The area at the base of a leaf, flower, fruit or other plant part containing tissues that play a role in the separation of a plant part from the main plant body. ATP (adenosine triphosphate): A nucleotide consisting of adenine, ribose sugar, and three phosphate groups; the major source of usable chemical energy in metabolism. On hydrolysis, ATP loses one phosphate to become adenosine diphosphate (ADP), releasing usable energy. ATP Synthase: An enzyme complex that forms ATP from ADP and phosphate during oxidative phos- phorylation in the inner mitochondrial membrane. During photosynthesis formed in the PS I photo-reaction: ADP + Pi → ATP Allelophathy: (Gk. allelon, of each + pathos, suffering) The inhibition of one species of plant by chemicals produced of another plant. Bacterium: An auto- or hetero-trophic prokaryotic organism. Cyanobacterium: Autotrophic organism capable of fixing nitrogen from air (heterocyst) and utilizing light energy to accomplish its energetical requirements. • Chloroplast: The thylakoids within the chloroplasts of cyanobateria are not stacked together in grana, but randomly distributed (lack PS II, cyclic photo-phosphorylation). Oxygenic photosynthetic reaction: CO2 + 2H2O → (Elight = h⋅f) → CH2O≈P → (CH2O)n + H2O + O2 • Heterocyst: Site of N2 fixation; a specially differentiated cells, working under anoxic onditions (H2 would combine
    [Show full text]