Check out our New Publishers' Select for Free Articles

BBA - Bioenergetics (v.1708, #2)

Editorial Board (pp. ii).

Characterization, structure and function of linker polypeptides in phycobilisomes of cyanobacteria and red algae: An overview by Lu-Ning Liu; Xiu-Lan Chen; Yu-Zhong Zhang; Bai-Cheng Zhou (pp. 133-142).

Cyanobacteria and red algae have intricate light-harvesting systems comprised of phycobilisomes that are attached to the outer side of the thylakoid membrane. The phycobilisomes absorb light in the wavelength range of 500–650 nm and transfer energy to the chlorophyll for photosynthesis. Phycobilisomes, which biochemically consist of phycobiliproteins and linker polypeptides, are particularly wonderful subjects for the detailed analysis of structure and function due to their spectral properties and their various components affected by growth conditions. The linker polypeptides are believed to mediate both the assembly of phycobiliproteins into the highly ordered arrays in the phycobilisomes and the interactions between the phycobilisomes and the thylakoid membrane. Functionally, they have been reported to improve energy migration by regulating the spectral characteristics of colored phycobiliproteins. In this review, the progress regarding linker polypeptides research, including separation approaches, structures and interactions with phycobiliproteins, as well as their functions in the phycobilisomes, is presented. In addition, some problems with previous work on linkers are also discussed.

Keywords: Abbreviations; LHC; light-harvesting complexes; PBS; phycobilisome; APC; allophycocyanin; PC; phycocyanin; PE; phycoerythrin; PEC; phycoerythrocyanin; PBP; phycobiliprotein; SDS-PAGE; sodium dodecyl sulfate-polyacrylamide gel electrophoresis; PEB; phycoerythrobilin; PUB; phycourobilinPhycobilisome; Linker polypeptide; Phycobiliprotein; Separation; Structure; Interaction; Function; γ Subunit

Distances between the b-subunits in the tether domain of F₀F₁-ATP synthase from E. coli by Stefan Steigmiller; Michael B�rsch; Peter Gr�ber; Martina Huber (pp. 143-153).

The arrangement of the b-subunits in the holo-enzyme F₀F₁-ATP synthase from E. coli is investigated by site-directed mutagenesis spin-label EPR. F₀F₁-ATP synthases couple proton translocation with the synthesis of ATP from ADP and phosphate. The hydrophilic F₁-part and the hydrophobic membrane-integrated F₀-part are connected by a central and a peripheral stalk. The peripheral stalk consists of two b-subunits. Cysteine mutations are introduced in the tether domain of the b-subunit at b-40, b-51, b-53, b-62 or b-64 and labeled with a nitroxide spin label. Conventional (9 GHz), high-field (95 GHz) and pulsed EPR spectroscopy reveal: All residues are in a relatively polar environment, with mobilities consistent with helix sites. The distance between the spin labels at each b-subunit is 2.9 nm in each mutant, revealing a parallel arrangement of the two helices. They can be in-register but separated by a large distance (1.9 nm), or at close contact and displaced along the helix axes by maximally 2.7 nm, which excludes an in-register coiled-coil model suggested previously for the b-subunit. Binding of the non-hydrolysable nucleotide AMPPNP to the spin-labeled enzyme had no significant influence on the distances compared to that in the absence of nucleotides.

Keywords: Abbreviations; AMPPNP; adenosine-5′-(β,γ-imido) triphosphate; DEER; double electron–electron resonance; EPR; electron paramagnetic resonance; MTSL; (1-oxyl-2,2,5,5-tetramethyl-Δ3-pyrroline-3-methyl) methanethiosulfonate; TMR-M; tetramethylrhodamine-5-maleimideH; ⁺; -ATP synthase; b-subunit; Site-directed spin labeling; MTSL; EPR spectroscopy; DEER

Photosystem I lacking the PSI-G subunit has a higher affinity for plastocyanin and is sensitive to photodamage by Agnieszka Zygadlo; Poul Erik Jensen; Dario Leister; Henrik Vibe Scheller (pp. 154-163).

PSI-G is an 11 kDa subunit of PSI in photosynthetic eukaryotes. Arabidopsis thaliana plants devoid of PSI-G have a decreased PSI content and an increased activity of NADP⁺ photoreduction in vitro but otherwise no obvious phenotype [P.E. Jensen, L. Rosgaard, J. Knoetzel, H.V. Scheller, Photosystem I activity is increased in the absence of the PSI-G subunit. J. Biol. Chem. 277, (2002) 2798–2803.]. To investigate the biochemical basis for the increased activity, the kinetic parameters of the reaction between PSI and plastocyanin were determined. PSI-G clearly plays a role in the affinity for plastocyanin since the dissociation constant ( K_D) is only 12 μM in the absence of PSI-G compared to 32 μM for the wild type. On the physiological level, plants devoid of PSI-G have a more reduced Q_A. This indicates that the decreased PSI content is due to unstable PSI rather than an adaptation to the increased activity. In agreement with this indication of decreased stability, plants devoid of PSI-G were found to be more photoinhibited both at low temperature and after high light treatment. The decreased PSI stability was confirmed in vitro by measuring PSI activity after illumination of a thylakoid suspension which clearly showed a faster decrease in PSI activity in the thylakoids lacking PSI-G. Light response of the P700 redox state in vivo showed that in the absence of PSI-G, P700 is more reduced at low light intensities. We conclude that PSI-G is involved in the binding dynamics of plastocyanin to PSI and that PSI-G is important for the stability of the PSI complex.

Keywords: Photosynthesis; Plastocyanin kinetic; Photosystem I; Photoinhibition

Quantitative mathematical expressions for accurate in vivo assessment of cytosolic [ADP] and Δ G of ATP hydrolysis in the human brain and skeletal muscle by Stefano Iotti; Chiara Frassineti; Antonio Sabatini; Alberto Vacca; Bruno Barbiroli (pp. 164-177).

Magnetic Resonance Spectroscopy affords the possibility of assessing in vivo the thermodynamic status of living tissues. The main thermodynamic variables relevant for the knowledge of the health of living tissues are: Δ G of ATP hydrolysis and cytosolic [ADP], the latter as calculated from the apparent equilibrium constant of the creatine kinase reaction. In this study we assessed the stoichiometric equilibrium constant of the creatine kinase reaction by in vitro³¹P NMR measurements and computer calculations resulting to be: log K_CK=8.00±0.07 at T=310 K and ionic strength I=0.25 M. This value refers to the equilibrium:PCr²⁻+ADP³⁻+H⁺=Cr+ATP⁴⁻ We also assessed by computer calculation the stoichiometric equilibrium constant of ATP hydrolysis obtaining the value: log K_ATP-hyd=−12.45 at T=310 K and ionic strength I=0.25 M, which refers to the equilibrium:ATP⁴⁻+H₂O=ADP³⁻+PO₄³⁻+2H⁺ Finally, we formulated novel quantitative mathematical expressions of Δ G of ATP hydrolysis and of the apparent equilibrium constant of the creatine kinase reaction as a function of total [PCr], pH and pMg, all quantities measurable by in vivo³¹P MRS. Our novel mathematical expressions allow the in vivo assessment of cytosolic [ADP] and Δ G of ATP hydrolysis in the human brain and skeletal muscle taking into account pH and pMg changes occurring in living tissues both in physiological and pathological conditions.

Keywords: Δ; G; ATP hydrolysis; Creatine kinase reaction; Magnesium; ³¹; P MRS; In vivo magnetic resonance spectroscopy; Apparent equilibrium constant

Species-specific modulation of the mitochondrial permeability transition by norbormide by Fernanda Ricchelli; Federica Dabbeni-Sala; Valeria Petronilli; Paolo Bernardi; Brian Hopkins; Sergio Bova (pp. 178-186).

In the present study, we show that norbormide stimulates the opening of the permeability transition pore (PTP) in mitochondria from various organs of the rat but not of guinea pig and mouse. Norbormide does not affect the basic parameters that modulate the PTP activity since the proton electrochemical gradient, respiration, phosphorylation and Ca²⁺ influx processes are only partially affected. On the other hand, norbormide induces rat-specific changes in the fluidity of the lipid interior of mitochondrial membranes, as revealed by fluorescence anisotropy of various reporter molecules. Such changes increase the PTP open probability through the internal Me²⁺ regulatory site. The lack of PTP opening by norbormide is matched by a negligible perturbation of internal lipid domains in guinea pig and mouse, suggesting that the drug does not gain access to the matrix in the mitochondria from these species. Consistent with this interpretation, we demonstrate a preferential interaction of norbormide with the mitochondrial surface leading to alterations of the Me²⁺ binding affinity for the external PTP regulatory site. Our findings indicate that norbormide affects Me²⁺ binding to the regulatory sites of the PTP, and suggest that the drug could be taken up by a mitochondrial transport system unique to the rat. The characterization of the norbormide target may lead to a better understanding of the mechanisms underlying the mitochondrial PTP as well as to the identification of species-specific drugs that affect mitochondrial function.

Keywords: Abbreviations; ANS; 8-anilino-1-naphthalene sulfonic acid; CsA; cyclosporine A; DPH; 1,6-diphenyl-1,3,5-hexatriene; FCCP; carbonylcyanide-; p; -trifluoromethoxyphenyl hydrazone; Laurdan; 6-dodecanoyl-2-dimethyl-aminonaphthalene; MOPS; 4-morpholinepropanesulfonic acid; Norbormide; [5-(α-hydroxy-α-2-pyridylbenzyl)-7-(α-2pyridylbenzylidene)-5-norbornene-2,3-dicarboximide]; RR; ruthenium red; PTP; permeability transition pore; r; fluorescence anisotropyMitochondria; Norbormide; Permeability transition; Species-specificity

Entropy-assisted stacking of thylakoid membranes by Eun-Ha Kim; Wah Soon Chow; Peter Horton; Jan M. Anderson (pp. 187-195).

Chloroplasts in plants and some green algae contain a continuous thylakoid membrane system that is structurally differentiated into stacked granal membranes interconnected by unstacked thylakoids, the stromal lamellae. Experiments were conducted to test the hypothesis that the thermodynamic tendency to increase entropy in chloroplasts contributes to thylakoid stacking to form grana. We show that the addition of bovine serum albumin or dextran, two very different water-soluble macromolecules, to a suspension of envelope-free chloroplasts with initially unstacked thylakoids induced thylakoid stacking. This novel restacking of thylakoids occurred spontaneously, accompanied by lateral segregation of PSII from PSI, thereby mimicking the natural situation. We suggest that such granal formation, induced by the macromolecules, is partly explained as a means of generating more volume for the diffusion of macromolecules in a crowded stromal environment, i.e., greater entropy overall. This mechanism may be relevant in vivo where the stroma has a very high concentration of enzymes of carbon metabolism, and where high metabolic fluxes are required.

Keywords: Abbreviations; ATP; adenosine triphosphate; BSA; bovine serum albumin; Chl; chlorophyll; Fm; maximal PSII fluorescence yield when the traps are closed; HEPES; N; -2-hydroxyethylpiperazine-; N; ′-2-ethansulfoinc acid; PSII; Photosystem II; PSI; Photosystem I; Rubisco; ribulose 1,5-bisphosphate carboxylase/oxygenaseChloroplast ultrastructure; Depletion attraction; Entropy; Grana; Macromolecular crowding; Thylakoid stacking

Interaction between subunit C (Vma5p) of the yeast vacuolar ATPase and the stalk of the C-depleted V₁ ATPase from Manduca sexta midgut by Yuriy L. Chaban; Sandra Juliano; Egbert J. Boekema; Gerhard Gr�ber (pp. 196-200).

Projection maps of a V₁–Vma5p hybrid complex, composed of subunit C (Vma5p) of Saccharomyces cerevisiae V-ATPase and the C-depleted V₁ from Manduca sexta, were determined from single particle electron microscopy. V₁–Vma5p consists of a headpiece and an elongated wedgelike stalk with a 2.1×3.0 nm protuberance and a 9.5×7.5 globular domain, interpreted to include Vma5p. The interaction face of Vma5p in V₁ was explored by chemical modification experiments.

Keywords: V-ATPase; V; ₁; V; _O; ATPase; V; ₁; ATPase; Vma5p; Reversible disassembly; Electron microscopy; Manduca sexta; Saccharomyces cerevisiae

Cellular energization protects the photosynthetic machinery against salt-induced inactivation in Synechococcus by Suleyman I. Allakhverdiev; Vyacheslav V. Klimov; Martin Hagemann (pp. 201-208).

The effects of the energization of cells by light and by exogenous glucose on the salt-induced inactivation of the photosynthetic machinery were investigated in the cyanobacterium Synechococcus sp. PCC 7942. The incubation of the cyanobacterial cells in a medium supplemented with 0.5 M NaCl induced a rapid decline with a subsequent slow decline, in the oxygen-evolving activity of Photosystem (PS) II and in the electron-transport activity of PSI. Light and exogenous glucose each protected PSII and PSI against the second phase of the NaCl-induced inactivation. The protective effects of light and glucose were eliminated by an uncoupler of phosphorylation and by lincomycin, an inhibitor of protein synthesis. Light and glucose had similar effects on the NaCl-induced inactivation of Na⁺/H⁺ antiporters. After photosynthetic and Na⁺/H⁺-antiport activities had been eliminated by the exposure of cells to 0.5 M NaCl in the darkness, both activities were partially restored by light or exogenous glucose. This recovery was prevented by lincomycin. These observations suggest that cellular energization by either photosynthesis or respiration, which is necessary for protein synthesis, is important for the recovery of the photosynthetic machinery and Na⁺/H⁺ antiporters from inactivation by a high level of NaCl.

Keywords: Abbreviations; BQ; 1,4-benzoquinone; CCCP; carbonyl cyanide; m; -chlorophenylhydrazone; Chl; chlorophyll; DAD; 2,3,5,6-tetramethyl-1.4-phenylenediamine; DCMU; 3-(3′,4′-dichlorophenyl)-1,1-dimethylurea; MV; methyl viologen; PS; photosystemSalt stress; Cellular energization; Photosynthesis; Respiration; Na; ⁺; /H; ⁺; -antiporter; Synechococcus

Energetics of primary and secondary electron transfer in Photosystem II membrane particles of spinach revisited on basis of recombination-fluorescence measurements by Markus Grabolle; Holger Dau (pp. 209-218).

Photon absorption by one of the roughly 200 chlorophylls of the plant Photosystem II (PSII) results in formation of an equilibrated excited state (Chl200*) and is followed by chlorophyll oxidation (formation of P680+) coupled to reduction of a specific pheophytin (Phe), then electron transfer from Phe− to a firmly bound quinone (QA), and subsequently reduction of P680+ by a redox-active tyrosine residue denoted as Z. The involved free-energy differences (Δ G) and redox potentials are of prime interest. Oxygen-evolving PSII membrane particles of spinach were studied at 5 °C. By analyzing the delayed and prompt Chl fluorescence, we determined the equilibrium constant and thus free-energy difference between Chl200* and the [Z+,QA−] radical pair to be −0.43±0.025 eV, at 10 μs after the photon absorption event for PSII in its S₃-state. On basis of this value and previously published results, the free-energy difference between P680* and [P680+,QA−] is calculated to be −0.50±0.04 eV; the free-energy loss associated with electron transfer from Phe to QA is found to be 0.34±0.04 eV. The given uncertainty ranges do not represent a standard deviation or likely error, but an estimate of the maximal error. Assuming a QA−/QA redox potential of −0.08 V [Krieger et al., 1995, Biochim. Biophys. Acta 1229, 193], the following redox-potential estimates are obtained: +1.25 V for P680/P680+; +1.21 V for Z/Z+ (at 10 μs); −0.42 V for Phe−/Phe; −0.58 V for P680*/P680+.

Keywords: Abbreviations; Chl; chlorophyll; DCBQ; 2,6-Dichloro-1,4-benzoquinone; DCMU; 3-(3,4-Dichlorophenyl)-1,1-Dimethylurea; EPPS; 4-(2-Hydroxyethyl)piperazine-1-propanesulfonic acid; ET; electron transfer; F; _D; delayed fluorescence signal; F; _P; prompt fluorescence signal; F; _M; maximum level of prompt fluorescence; F; ₀; minimum level of prompt fluorescence; Δ; G; difference in Gibbs free energy; MES; 2-Morpholinoethanesulfonic acid; MOPS; 3-Morpholinopropanesulfonic acid; P680; primary chlorophyll donor in PSII; Phe; specific pheophytin of PSII; PM; photomultiplier; PSII; Photosystem II; Q; _A; primary quinone acceptor of PSII; Q; _B; secondary quinone acceptor of PSII; Z or Y; _Z; or Tyr; _Z; Tyr-160/161 of the D1 protein of PSIIChlorophyll fluorescence; Delayed fluorescence; P680; Oxygenic photosynthesis; Redox potential

Extinction coefficients and critical solubilisation concentrations of photosystems I and II from Thermosynechococcus elongatus by Frank M�h; Athina Zouni (pp. 219-228).

The absorption properties of chlorophyll a (Chl a) in active core complexes of photosystems I (PSI) and II (PSII) isolated in high purity from the thermophilic cyanobacterium Thermosynechococcus elongatus were correlated with those of extracts in 80% acetone to determine effective extinction coefficients of protein-bound Chl a and molar extinction coefficients of core complexes and reaction centers (RC). These coefficients allow a quick determination of Chl a and protein concentrations from steady-state absorption spectra of intact samples without the need for pigment extraction and protein destruction. In the visible range, ε₆₈₀^p = 57 mM⁻¹ cm⁻¹ for trimeric PSI (PSIt) and ε₆₇₄^p = 70 mM⁻¹ cm⁻¹ for dimeric (PSIId) and monomeric (PSIIm) PSII (error ±6%; superscript “ p�? refers to Chl a bound to intact protein, subscripts are the peak maxima in nm). The integral extinction coefficient ϕ^p = 2.8 nm μM⁻¹ cm⁻¹ for the wavelength interval between 550 and 800 nm and the extinction coefficient ε_B^p = 14 mM⁻¹ cm⁻¹ for the smaller absorption maximum (B = 632 nm for PSI and 627 nm for PSII) were found to be essentially the same for both types of PS. The coefficients of PSIt are shown to remain unaltered when 65% (v/v) of the buffer is replaced with glycerol. Molar extinction coefficients of core complexes were determined using Chl a/RC ratios of 96±1 for PSI and 35±2 for PSII based on X-ray data. In addition, the critical solubilisation concentration of n-dodecyl-β-d-maltoside (βDM), necessary to keep the core complexes in solution, was determined by turbidimetric titrations. It was found that at least ∼500 βDM molecules per PSIt (∼2 βDM per Chl a) and 190 βDM molecules per PSIIm (∼5 βDM per Chl a, also for PSIId) in excess of the critical micelle concentration of 0.16 ± 0.03 mM are necessary for a complete solubilisation of the core complexes.

Keywords: Abbreviations; Chl; chlorophyll; CMC; critical micelle concentration; CSC; critical solubilisation concentration; βDM; n; -dodecyl-β-; d; -maltoside; Pheo; pheophytin; PS; photosystem; PSIt; trimeric photosystem I core complex; PSIIm; monomeric photosystem II core complex; PSIId; dimeric photosystem II core complex; PPC; pigment–protein complex; RC; reaction centerChlorophyll determination; Critical solubilisation concentration; Detergent–protein ratio; Extinction coefficient; Photosystem I; Photosystem II

Overexpression and characterization of dark-operative protochlorophyllide reductase from Rhodobacter capsulatus by Jiro Nomata; Lee R. Swem; Carl E. Bauer; Yuichi Fujita (pp. 229-237).

Dark-operative protochlorophyllide oxidoreductase (DPOR) plays a crucial role in light-independent (bacterio)chlorophyll biosynthesis in most photosynthetic organisms. However, the biochemical properties of DPOR are still largely undefined. Here, we constructed an overexpression system of two separable components of DPOR, L-protein (BchL) and NB-protein (BchN-BchB), in the broad-host-range vector pJRD215 in Rhodobacter capsulatus. We established a stable DPOR assay system by mixing crude extracts from the two transconjugants under anaerobic conditions. Using this assay system, we demonstrated some basic properties of DPOR. The Km value for protochlorophyllide was 10.6 μM. Ferredoxin functioned as an electron donor to DPOR. Elution profiles in gel filtration chromatography indicated that L-protein and NB-protein are a homodimer [(BchL)₂] and a heterotetramer [(BchN)₂(BchB)₂], respectively. These results provide a framework for the characterization of these components in detail, and further support a nitrogenase model of DPOR.

Keywords: Bacteriochlorophyll biosynthesis; Ferredoxin; Light-independent protochlorophyllide reductase; Nitrogenase-like enzyme; Protochlorophyllide reduction; Rhodobacter capsulatus

EPR study of electron transport in the cyanobacterium Synechocystis sp. PCC 6803: Oxygen-dependent interrelations between photosynthetic and respiratory electron transport chains by Boris V. Trubitsin; Vasilii V. Ptushenko; Olga A. Koksharova; Mahir D. Mamedov; Liya A. Vitukhnovskaya; Igor A. Grigor'ev; Alexey Yu. Semenov; Alexander N. Tikhonov (pp. 238-249).

In this work, we investigated electron transport processes in the cyanobacterium Synechocystis sp. PCC 6803, with a special emphasis focused on oxygen-dependent interrelations between photosynthetic and respiratory electron transport chains. Redox transients of the photosystem I primary donor P700 and oxygen exchange processes were measured by the EPR method under the same experimental conditions. To discriminate between the factors controlling electron flow through photosynthetic and respiratory electron transport chains, we compared the P700 redox transients and oxygen exchange processes in wild type cells and mutants with impaired photosystem II and terminal oxidases ( CtaI, CydAB, CtaDEII). It was shown that the rates of electron flow through both photosynthetic and respiratory electron transport chains strongly depended on the transmembrane proton gradient and oxygen concentration in cell suspension. Electron transport through photosystem I was controlled by two main mechanisms: (i) oxygen-dependent acceleration of electron transfer from photosystem I to NADP⁺, and (ii) slowing down of electron flow between photosystem II and photosystem I governed by the intrathylakoid pH. Inhibitor analysis of P700 redox transients led us to the conclusion that electron fluxes from dehydrogenases and from cyclic electron transport pathway comprise 20–30% of the total electron flux from the intersystem electron transport chain to P700⁺.

Keywords: Abbreviations; PS I and PS II; Photosystem I and photosystem II, respectively; P700; primary electron donor of photosystem I; PQ; plastoquinone; PQH; ₂; plastoquinol; NDH-1; type I NADPH dehydrogenase; SDH; succinate dehydrogenase; Cyt; cytochrome; EPR; electron paramagnetic resonance; DCMU; 3-(3,4-dichloro-phenyl)-1, 1-dimethylurea; DBMIB; 2,5-dibromo-3-methyl-6-isopropyl-; p; -benzoquinone; CCCP; carbonylcyanide-3-chlorophenyl hydrazone; TCPO; 2,2,5,5-tetramethyl-3-carboxy-pyrroline-1-oxyl; WT; wild type; Ox; ⁻; oxidase-deficient mutantCyanobacteria; Electron transport control; Electron paramagnetic resonance

A cell-based model for the photoacclimation and CO₂-acclimation of the photosynthetic apparatus by I.A. Papadakis; K. Kotzabasis; K. Lika (pp. 250-261).

We have developed a mathematical model based on the underlying mechanisms concerning the responses of the photosynthetic apparatus of a microalga cell which grows under constant incident light intensity and ambient CO₂ concentration. Photosynthesis involves light and carbon-fixation reactions which are mutually dependent and affect each other, but existing models for photosynthesis don't account for both reactions at once. Our modeling approach allows us to derive distinct equations for the rates of oxygen production, NADPH production, carbon dioxide fixation, carbohydrate production, and rejected energy, which are generally different. The production rates of the photosynthesis products are hyperbolic functions of light and CO₂ concentration. The model predicts that in the absence of photoinhibition, CO₂-inhibition, photorespiration, and chlororespiration, a cell acclimated to high light and/or CO₂ concentration has higher photosynthetic capacity and lower photosynthetic efficiency than does a cell acclimated to low conditions. This results in crossing between the two curves which represent the oxygen production rates and carbon fixation rates in low and high conditions. Finally, in the absence of photoinhibition and CO₂-inhibition, the model predicts the carbohydrate production rate in terms of both light intensity and CO₂ concentration.

Keywords: Photosynthesis; Light reaction; Carbon-fixation reaction; Mathematical model; Synthesizing unit

A four-subunit cytochrome bc₁ complex complements the respiratory chain of Thermus thermophilus by Daniela Mooser; Oliver Maneg; Carsten Corvey; Thomas Steiner; Francesco Malatesta; Michael Karas; Tewfik Soulimane; Bernd Ludwig (pp. 262-274).

Several components of the respiratory chain of the eubacterium Thermus thermophilus have previously been characterized to various extent, while no conclusive evidence for a cytochrome bc₁ complex has been obtained. Here, we show that four consecutive genes encoding cytochrome bc₁ subunits are organized in an operon-like structure termed fbcCXFB. The four gene products are identified as genuine subunits of a cytochrome bc₁ complex isolated from membranes of T. thermophilus. While both the cytochrome b and the FeS subunit show typical features of canonical subunits of this respiratory complex, a further membrane-integral component (FbcX) of so far unknown function copurifies as a subunit of this complex. The cytochrome c₁ carries an extensive N-terminal hydrophilic domain, followed by a hydrophobic, presumably membrane-embedded helical region and a typical heme c binding domain. This latter sequence has been expressed in Escherichia coli, and in vitro shown to be a kinetically competent electron donor to cytochrome c₅₅₂, mediating electron transfer to the ba₃ oxidase. Identification of this cytochrome bc₁ complex bridges the gap between the previously reported NADH oxidation activities and terminal oxidases, thus, defining all components of a minimal, mitochondrial-type electron transfer chain in this evolutionary ancient thermophile.

Keywords: Abbreviations; ET; electron transfer; aa; amino acid; ORF; open reading frame; I; ionic strength; MALDI; matrix-assisted laser desorption ionization; TOF; time of flight; MS; mass spectrometry; AP; atmospheric pressure; TMPD; tetramethyl-p-phenylendiamine; IPTG; isopropyl β-; d; -thiogalactopyranoside; NDH-1; NADH:quinone oxidoreductase-1 (energy transducing); NDH-2; NADH:quinone oxidoreductase-2; PSD; post source decay, spectrometer; MK-8; menaquinone-8 Thermus thermophilus; Respiratory chain; Cytochrome; bc; ₁; Complex III; Electron transfer; Stopped flow kinetics

In intact leaves, the maximum fluorescence level ( F_M) is independent of the redox state of the plastoquinone pool: A DCMU-inhibition study by Szilvia Z. T�th; Gert Schansker; Reto J. Strasser (pp. 275-282).

The effects of DCMU (3-(3′,4′-dichlorophenyl)-1,1-dimethylurea) on the fluorescence induction transient (OJIP) in higher plants were re-investigated. We found that the initial ( F₀) and maximum ( F_M) fluorescence levels of DCMU-treated leaves do not change relative to controls when the treatment is done in complete darkness and DCMU is allowed to diffuse slowly into the leaves either by submersion or by application via the stem. Simultaneous 820 nm transmission measurements (a measure of electron flow through Photosystem I) showed that in the DCMU-treated samples, the plastoquinone pool remained oxidized during the light pulses whereas in uninhibited leaves, the F_M level coincided with a fully reduced electron transport chain. The identical F_M values with and without DCMU indicate that in intact leaves, the F_M value is independent of the redox state of the plastoquinone pool. We also show that (i) the generally observed F₀ increase is probably due to the presence of (even very weak) light during the DCMU treatment, (ii) vacuum infiltration of leaf discs leads to a drastic decrease of the fluorescence yield, and in DCMU-treated samples, the F_M decreases to the I-level of their control (leaves vacuum infiltrated with 1% ethanol), (iii) and in thylakoid membranes, the addition of DCMU lowers the F_M relative to that of a control sample.

Keywords: Abbreviations; ABS/CS; absorption flux per CS; ABS/RC; absorption flux per RC; chl; chlorophyll; CS; cross section; DCMU; 3-(3′,4′-dichlorophenyl)-1,1-dimethylurea; ET; ₀; /CS; electron transport flux per CS (at; t; =; 0); ET; ₀; /RC; electron transport flux per RC (at; t; =; 0); F; ₀; initial fluorescence, fluorescence intensity at 20 μs; F; _M; maximum fluorescence; J- and I-steps; fluorescence intensities at around 2 and 30 ms, respectively; LED; light-emitting diode; LHCII; light-harvesting chlorophyll; a; /; b; protein complex of PSII; PC; plastocyanin; PQ; plastoquinone; PSI; Photosystem I; PSII; Photosystem II; P680 and P700; reaction center chlorophylls of PSII and PSI, respectively; Q; _A; and Q; _B; primary and secondary quinones of PSII, respectively; RC; reaction center; TR; ₀; /CS; trapped energy flux per CS (at; t; =; 0); TR; ₀; /RC; trapped energy flux per RC (at; t; =; 0); ψ; ₀; probability (at time 0) that a trapped exciton moves an electron into the electron transport chain beyond Q; _A; ^-; φ; _Po; maximum quantum yield for primary photochemistryChlorophyll; a; fluorescence; DCMU; OJIP transient; Plastoquinone pool quenching; 820 nm transmission

Sections

Personal tools

BBA - Bioenergetics (v.1708, #2)

Sections

Personal tools

Local resources

BBA - Bioenergetics (v.1708, #2)