Forgot your password?
New user?
New Window Opens on the Secret Life of Microbes: Scientists Develop First Microbial Profiles of Ecosystems
CAS announces the release of SciFinder Scholar for Mac OS X
Press Releases
Press Releases
| Check out our New Publishers' Select for Free Articles |
BBA - Bioenergetics (v.1827, #1)
The fifth electron in the fully reduced caa3 from Thermus thermophilus is competent in proton pumping by Sergey A. Siletsky; Ilya Belevich; Tewfik Soulimane; Michael I. Verkhovsky; Wikstrom Mårten Wikström (pp. 1-9).
The time-resolved kinetics of membrane potential generation coupled to oxidation of the fully reduced (five-electron) caa3 cytochrome oxidase from Thermus thermophilus by oxygen was studied in a single-turnover regime. In order to calibrate the number of charges that move across the vesicle membrane in the different reaction steps, the reverse electron transfer from heme a3 to heme a and further to the cytochrome c/CuA has been resolved upon photodissociation of CO from the mixed valence enzyme in the absence of oxygen. The reverse electron transfer from heme a3 to heme a and further to the cytochrome c/CuA pair is resolved as a single transition with τ~40μs. In the reaction of the fully reduced cytochrome caa3 with oxygen, the first electrogenic phase (τ~30μs) is linked to OO bond cleavage and generation of thePR state. The next electrogenic component (τ~50μs) is associated with thePR→F transition and together with the previous reaction step it is coupled to translocation of about two charges across the membrane. The three subsequent electrogenic phases, with time constants of ~0.25ms, ~1.4ms and ~4ms, are linked to the conversion of the binuclear center through theF→OH→EH transitions, and result in additional transfer of four charges through the membrane dielectric. This indicates that the delivery of the fifth electron from heme c to the binuclear center is coupled to pumping of an additional proton across the membrane.► We have resolved kinetics of membrane potential generation by caa3 cytochrome oxidase. ► Single-turnover oxidation of the fully reduced enzyme by oxygen was studied. ► The number of charges translocated coupled to the different reaction steps were identified. ► Delivery of the fifth electron to the catalytic center is coupled to proton pumping.
Keywords: Abbreviations; BNC; binuclear heme; a; 3; /Cu; B; center; HEPES; 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid; MV-CO; the “mixed valence” state with bound CO; SHE; standard hydrogen electrode; RuAm; hexammineruthenium; TMPD; N,N,N′; ,; N′; -tetramethyl-1,4-phenylenediamine; τ; time constant; E; m; midpoint redox potential versus SHE; E; h; ambient redox potential versus SHE; DM; (dodecyl L-D-maltoside)Cytochrome; c; oxidase; Charge transfer steps; Catalytic cycle intermediates; Membrane potential; Thermus thermophilus
Variations in the first steps of photosynthesis for the diatom Cyclotella meneghiniana grown under different light conditions by V.U. Chukhutsina; Buchel C. Büchel; H. van Amerongen (pp. 10-18).
In this work we have applied picosecond and steady-state fluorescence measurements to study excitation energy transfer and trapping in intact Cyclotella meneghiniana diatom cells grown at different light intensities. Different excitation and detection wavelengths were used to discriminate between Photosystem I and II (PSI and PSII) kinetics and to study excitation energy transfer from the outer antenna to the core of PSI and PSII. It is found that the light-harvesting fucoxanthin chlorophyll proteins (FCPs) transfer their excitation energy predominantly to PSII. It is also observed that the PSII antenna is slightly richer in red-absorbing fucoxanthin than the FCPs associated with PSI. The average excitation trapping time in PSI is around 75ps whereas this time is around 450ps for PSII in cells grown in 20μmol of photons per m2 per s. The latter time decreases to 425ps for 50μmol of photons and 360ps for 140μmol of photons. It is concluded that cells grown under higher photon flux densities have a smaller antenna size than the ones grown in low light. At the same time, the increase of growth light intensity leads to a decrease of the relative amount of PSI. This effect is accompanied by a substantial increase in the amount of chlorophyll a that is not active in excitation energy transfer and most probably attached to inactivated/disassembled PSII units.► Separation of picosecond fluorescence kinetics of photosystems I and II of diatoms. ► Spectral separation of PSI and PSII. ► Antenna of diatoms transfers excitations mainly to PSII. ► Higher growth irradiance leads to smaller PSII antenna. ► Higher growth irradiance leads to substantial amounts of inactive chlorophyll.
Keywords: Abbreviations; Chl; chlorophyll; DAS; decay-associated spectra; ddx; diadinoxanthin; dtx; diatoxanthin; EET; excited state absorption; FCP; fucoxanthin-chlorophyll a/c; 1,2; protein; fx; fucoxanthin; fx; blue; blue-absorbing fucoxanthin; fx; red; red-absorbing fucoxanthin; FWHM; the full-width at half-maximum; ICT; intramolecular charge transfer; LHC; light-harvesting chlorophyll protein; NPQ; nonphotochemical quenching; OD; optical density; PS; photosystem; PSU; photosynthetic unit; RC; reaction center; TCSPC; Time-correlated single photon countingTime-resolved fluorescence; Fucoxanthin-chlorophyll protein; Light harvesting; Photosystem I; Photosystem II; Excitation energy transfer
‘Domino’ systems biology and the ‘A’ of ATP by Malkhey Verma; Maksim Zakhartsev; Matthias Reuss; Hans V. Westerhoff (pp. 19-29).
We develop a strategic ‘domino’ approach that starts with one key feature of cell function and the main process providing for it, and then adds additional processes and components only as necessary to explain provoked experimental observations. The approach is here applied to the energy metabolism of yeast in a glucose limited chemostat, subjected to a sudden increase in glucose. The puzzles addressed include (i) the lack of increase in Adenosine triphosphate (ATP) upon glucose addition, (ii) the lack of increase in Adenosine diphosphate (ADP) when ATP is hydrolyzed, and (iii) the rapid disappearance of the ‘A’ (adenine) moiety of ATP. Neither the incorporation of nucleotides into new biomass, nor steady de novo synthesis of Adenosine monophosphate (AMP) explains. Cycling of the ‘A’ moiety accelerates when the cell's energy state is endangered, another essential domino among the seven required for understanding of the experimental observations. This new domino analysis shows how strategic experimental design and observations in tandem with theory and modeling may identify and resolve important paradoxes. It also highlights the hitherto unexpected role of the ‘A’ component of ATP.► A novel ‘domino’ systems biology approach is developed to explain ATP paradox. ► Domino systems biology starts with a key feature of cell function and main process. ► More processes are added only as needed to explain experimental observations. ► Domino approach explains rapid disappearance of ATP in glucose perturbed yeast. ► It explains new role of the adenine of ATP in energy endangered states of cell.
Keywords: Domino systems biology; Domino process; Glycolysis; Adenine nucleotide; IMP salvage; Saccharomyces cerevisiae
Molecular symmetry determines the mechanism of a very efficient ultrafast excitation-to-heat conversion in Ni-substituted chlorophylls by Mariusz Pilch; Alina Dudkowiak; Barbara Jurzyk; Lukasiewicz Jędrzej Łukasiewicz; Anna Susz; Grażyna Stochel; Leszek Fiedor (pp. 30-37).
In the Ni-substituted chlorophylls, an ultrafast (<60fs) deactivation channel is created, which is not present in Ni-porphyrins. This observation prompted us to investigate in detail the mechanism of excitation-to-heat conversion in Ni-substituted chlorophylls, experimentally, using time-resolved laser-induced optoacoustic spectroscopy, and theoretically, using group theory approach. The Ni-substituted chlorophylls show exceptional photostability and the optoacoustic measurements confirm the prompt and very efficient (100%) excitation-into-heat conversion in these complexes. Considering their excellent spectral properties and the loss-free excitation-into-heat conversion they are likely to become a new class of versatile photocalorimetric references. The curious features of the Ni-substituted chlorophylls originate from the symmetry of a ligand field created in the central cavity. The central NNi2+ bonds, formed via the donation of two electrons from each of the sp2 orbitals of two central nitrogens to an emptys−dx2−y2 hybrid centered on Ni2+, have a considerable covalent character. The extreme rate of excited state relaxation is then not due to a ladder of the metal centered d-states, often invoked in metalloporphyrins, but seems to result from a peculiar topology of the potential energy surface (a saddle-shaped crossing) due to the covalent character of the NNi2+ bonds. This is confirmed by a strong 0→0 character of electronic transitions in these complexes indicating a similarity of their equilibrium geometries in the ground (S0) and the excited states (both QX and QY). The excitation energy is very efficiently converted into molecular vibrations and dissipated as heat, involving the central Ni2+. These Ni-substituted pigments pose a fine exemplification of symmetry control over properties of excited states of transition metal complexes.MS: molecular symmetry determines the mechanism of a very efficient ultrafast excitation-to-heat conversion in Ni-substituted chlorophylls, by Fiedor et al.Display Omitted► Local symmetry controls the fate of excited state in the Ni-substituted macrocycles. ► An unexpected type of a strong three-center bond between Ni2+ and nitrogens is formed in the central binding pocket of Chl. ► Ni-substituted Chls are a new class of photocalorimetric references. ► Generalizations based on the systems of higher symmetries have to be applied very cautiously to the ones of lower symmetry.
Keywords: Metallochlorophyll; Ultrafast relaxation; Central metal ion bonding; Photoacoustics; Photocalorimetric reference
Sirtuin-4 modulates sensitivity to induction of the mitochondrial permeability transition pore by Manish Verma; Nataly Shulga; John G. Pastorino (pp. 38-49).
The sustained opening of the mitochondrial permeability transition pore (PTP) is a decisive event in the onset of irreversible cell injury. The PTP is modulated by numerous exogenous and endogenous effectors, including mitochondrial membrane potential, ions and metabolites. Mitochondrial sirtuins have recently emerged as pivotal mediators of mitochondrial metabolism. In the present study, we demonstrate that sirt-4 modulates sensitivity to PTP onset induced by calcium and the oxidative cross linking reagent phenylarsine oxide, and PTP dependent cytotoxicity brought about by TNF or doxorubicin. Moreover, the ability of sirt-4 to modulate onset of the PTP is dependent on the expression of glutamate dehydrogenase-1.► Sirtuin-4 modulates sensitivity to the permeability transition pore. ► Depletion of sirtuin-4 enhances resistance to PTP induction. ► Expression of glutamate dehydrogenase-1 is required for sirtuin-4 to modulate PTP sensitivity. ► Sirtuin-4 mediates sensitivity to PTP dependent cytotoxicity.
Keywords: Sirtuin-4; Mitochondria; Permeability transition pore; Oxidative stress
Psb28 is involved in recovery of photosystem II at high temperature in Synechocystis sp. PCC 6803 by Shinya Sakata; Naoki Mizusawa; Hisako Kubota-Kawai; Isamu Sakurai; Hajime Wada (pp. 50-59).
Psb28 is an extrinsic protein of photosystem II (PSII), which is conserved among photosynthetic organisms from cyanobacteria to higher plants. A unicellular cyanobacterium, Synechocystis sp. PCC 6803, has two homologs of Psb28, Psb28-1 and Psb28-2. However, the role of these proteins remains poorly understood. In this study, we disrupted the psb28-1 ( sll1398) and psb28-2 ( slr1739) genes in wild-type Synechocystis sp. PCC 6803 and examined their photosynthetic properties to elucidate the physiological role of Psb28 in photosynthesis. We also disrupted the psb28-1 gene in a dgdA mutant defective in the biosynthesis of digalactosyldiacylglycerol, in which Psb28-1 significantly accumulates in PSII. The disruption of the psb28-1 gene in the wild-type resulted in growth retardation under high-light conditions at high temperatures with a low rate of restoration of photodamaged photosynthetic machinery. Similar phenomena were observed at normal growth temperatures in the psb28-1/dgdA double mutant. In contrast, disruption of psb28-2 in the wild-type and dgdA mutant did not affect host strain phenotype, suggesting that Psb28-2 does not contribute to the recovery of PSII. In addition, protein analysis using strains expressing His-tagged Psb28-1 revealed that Psb28-1 is mainly associated with the CP43-less PSII monomer. In the dgdA mutant, the CP43-less PSII monomer accumulated to a greater extent than in the wild-type, and its accumulation caused greater accumulation of Psb28-1 in PSII. These results demonstrate that Psb28-1 plays an important role in PSII repair through association with the CP43-less monomer, particularly at high temperatures.► psb28 mutants were constructed in the cyanobacterium Synechocystis sp. PCC 6803. ► Growth of psb28-1 mutant was retarded at high temperatures. ► psb28-1 mutant had a low rate of restoration of photosynthetic activities. ► psb28-2 mutant did not show significant phenotype. ► Psb28-1 is involved in recovery of photosystem II at high temperatures.
Keywords: Abbreviations; BN-PAGE; blue native-polyacrylamide gel electrophoresis; BQ; p; -benzoquinone; Chl; chlorophyll; Cm; R; chloramphenicol-resistant gene cassette; DCMU; 3-(3,4-dichlorophenyl)-1,1-dimethylurea; DGDG; digalactosyldiacylglycerol; Fecy; potassium ferricyanide; HL; high light; Km; R; kanamycin-resistant gene cassette; LL; low light; ML; moderate light; PCR; polymerase chain reaction; PG; phosphatidylglycerol; PSII; photosystem II; SDS–PAGE; SDS–polyacrylamide gel electrophoresisCyanobacterium; Photosynthesis; Photosystem II; Psb28; Synechocystis; sp. PCC 6803
Corrigendum to “The ζ subunit of the α-proteobacterial F1FO-ATP synthase in Paracoccus denitrificans: A novel control mechanism of the central rotor” [Biochim. Biophys. Acta 1817S (2012) S27–S28]
by M. Zarco-Zavala; Morales-Rios E. Morales-Ríos; P. Serrano-Navarro; Wuthrich K. Wüthrich; Mendoza-Hernandez G. Mendoza-Hernández; Ramirez-Silva L. Ramírez-Silva; Garcia-Trejo J.J. García-Trejo (pp. 60-60).