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151.
Boris V. Trubitsin Olga A. Koksharova Liya A. Vitukhnovskaya Alexey Yu. Semenov 《BBA》2005,1708(2):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+. 相似文献
152.
Mamedov MD Tyunyatkina AA Siletsky SA Semenov AY 《European biophysics journal : EBJ》2006,35(8):647-654
An electrometrical technique was used to investigate proton-coupled electron transfer between the primary plastoquinone acceptor QA− and the oxidized non-heme iron Fe3+ on the acceptor side of photosystem II core particles incorporated into phospholipid vesicles. The sign of the transmembrane electric potential difference Δψ (negative charging of the proteoliposome interior) indicates that the iron–quinone complex faces the interior surface of the proteoliposome membrane. Preoxidation of the non-heme iron was achieved by addition of potassium ferricyanide entrapped into proteoliposomes. Besides the fast unresolvable kinetic phase (τ ∼ 0.1 μs) of Δψ generation related to electron transfer between the redox-active tyrosine YZ and QA, an additional phase in the submillisecond time domain (τ ∼ 0.1 ms at 23°C, pH 7.0) and relative amplitude ∼ 20% of the amplitude of the fast phase was observed under exposure to the first flash. This phase was absent under the second laser flash, as well as upon the first flash in the presence of DCMU, an inhibitor of electron transfer between QA and the secondary quinone QB. The rate of the additional electrogenic phase is decreased by about one-half in the presence of D2O and is reduced with the temperature decrease. On the basis of the above observations we suggest that the submillisecond electrogenic reaction induced by the first flash is due to the vectorial transfer of a proton from external aqueous phase to an amino acid residue(s) in the vicinity of the non-heme iron. The possible role of the non-heme iron in cyclic electron transfer in photosystem II complex is discussed. 相似文献
153.
154.
Anastasia A. Petrova Baina K. Boskhomdzhieva Georgy E. Milanovsky Olga A. Koksharova Mahir D. Mamedov Dmitry A. Cherepanov Alexey Yu. Semenov 《Photosynthesis research》2017,133(1-3):175-184
Interaction of photosystem I (PS I) complexes from cyanobacteria Synechocystis sp. PCC 6803 containing various quinones in the A1-site (phylloquinone PhQ in the wild-type strain (WT), and plastoquinone PQ or 2,3-dichloronaphthoquinone Cl 2 NQ in the menB deletion strain) and different numbers of Fe4S4 clusters (intact WT and FX-core complexes depleted of FA/FB centers) with external acceptors has been studied. The efficiency of interaction was estimated by measuring the light-induced absorption changes at 820 nm due to the reduction of the special pair of chlorophylls (P700 +) by an external acceptor(s). It was shown that externally added Cl 2 NQ is able to effectively accept electrons from the terminal iron-sulfur clusters of PS I. Moreover, the efficiency of Cl 2 NQ as external acceptor was higher than the efficiency of the commonly used artificial electron acceptor, methylviologen (MV) for both the intact WT PS I and for the FX-core complexes. The comparison of the efficiency of MV interaction with different types of PS I complexes revealed gradual decrease in the following order: intact WT?>?menB?>?FX-core. The effect of MV on the recombination kinetics in menB complexes of PS I with Cl 2 NQ in the A1-site differed significantly from all other PS I samples. The obtained effects are considered in terms of kinetic efficiency of electron acceptors in relation to thermodynamic and structural characteristics of PS I complexes. 相似文献
155.
Effects of assortative mate choice on the genomic and morphological structure of a hybrid zone between two bird subspecies
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Georgy A. Semenov Elizabeth S. C. Scordato David R. Khaydarov Chris C. R. Smith Nolan C. Kane Rebecca J. Safran 《Molecular ecology》2017,26(22):6430-6444
Phenotypic differentiation plays an important role in the formation and maintenance of reproductive barriers. In some cases, variation in a few key aspects of phenotype can promote and maintain divergence; hence, the identification of these traits and their associations with patterns of genomic divergence is crucial for understanding the patterns and processes of population differentiation. We studied hybridization between the alba and personata subspecies of the white wagtail (Motacilla alba), and quantified divergence and introgression of multiple morphological traits and 19,437 SNP loci on a 3,000 km transect. Our goal was to identify traits that may contribute to reproductive barriers and to assess how variation in these traits corresponds to patterns of genome‐wide divergence. Variation in only one trait—head plumage patterning—was consistent with reproductive isolation. Transitions in head plumage were steep and occurred over otherwise morphologically and genetically homogeneous populations, whereas cline centres for other traits and genomic ancestry were displaced over 100 km from the head cline. Field observational data show that social pairs mated assortatively by head plumage, suggesting that these phenotypes are maintained by divergent mating preferences. In contrast, variation in all other traits and genetic markers could be explained by neutral diffusion, although weak ecological selection cannot be ruled out. Our results emphasize that assortative mating may maintain phenotypic differences independent of other processes shaping genome‐wide variation, consistent with other recent findings that raise questions about the relative importance of mate choice, ecological selection and selectively neutral processes for divergent evolution. 相似文献
156.
Semenov V. M. Kravchenko I. K. Kuznetsova T. V. Semenova N. A. Bykova S. A. Dulov L. E. Gal'chenko V. F. Pardini G. Gispert M. Boeckx P. Van Cleemput O. 《Microbiology》2004,73(3):356-362
Seasonal fluctuations in the methane fluxes in the soil–atmosphere system were determined for gray forest soils of Central Russia. Consumption of atmospheric methane was found to exceed methane emission in gray forest soils under forest and in the agrocenosis. The average annual rates of atmospheric methane consumption by the soil under forest and in the agrocenosis were 0.026 and 0.008 mg C-CH4/(m2 h), respectively. The annual rate of atmospheric methane oxidation in the gray forest soils of Moscow oblast was estimated to be 0.68 kton. Seasonal fluctuations in the methane oxidation activity were due to changes in the hydrothermal conditions and in the reserves of readily decomposable organic matter and mineral nitrogen, as well as to changes in the activity of methane oxidizers. 相似文献
157.
Long adaptation of microsporidia, a large group of fungi-related protozoa, to intracellular lifestyle has resulted in drastic minimization of a parasite cell. Thus, diversity of carbohydrates in microsporidia glycoproteins and proteoglycans is expected to be restricted by O-linked manno-oligosaccharides because three genes involved in O-mannosylation of proteins and no components of N-linked glycosylation machinery were found in genome of human pathogen Encephalitozoon cuniculi. In this study we investigated glycosylation of spore proteins of microsporidia Paranosema (Antonospora) grylli infecting crickets Gryllus bimaculatus. Using periodic acid-Shiff reagent staining we have demonstrated that some P. grylli spore proteins are highly-glycosylated. The major polar tube protein (PTP1) of 56 kDa was shown as the most intensively decorated band. The experiments with N-glycosidase F and WGA lectin did not reveal any N-glycosylated proteins in P. grylli spores. At the same time, incubation of major spore wall protein of 40 kDa (p40) with mannose specific lectin GNA resulted in specific binding that was reduced by pretreatment of the protein with mannosidases. Interestingly, in spite of PTP1 glycosylation, polar tube proteins extracted from P. grylli spores were not precipitated by GNA-agarose. Since P. grylli and E. cuniculi are distantly related, our data suggest that dramatic reduction of protein glycosylation machinery is a common feature of microsporidia. 相似文献
158.
Y Y Vengerov T E Semenov S A Streltsov V L Makarov A A Khorlin G V Gursky 《Journal of molecular biology》1985,184(2):251-255
Complexes of circular superhelical pBR322 DNA with a synthetic tripeptide capable of beta-structure formation (dansylhydrazide trivaline) were studied at different peptide/DNA ratios by electron microscopy. It was shown on rotary-shadowed preparations that peptide binding induces intramolecular DNA condensation and compact ring-shaped particles are formed from fibres 120 A thick. The analysis of the morphology of the ring structures observed at various peptide/DNA ratios as well as contour length measurements enabled us to draw conclusions about the organization of the double-stranded DNA filaments in these structures. It was established that the fibres forming compact rings contain three double-stranded DNA segments closely associated due to DNA-peptide and peptide-peptide interactions. The mechanisms leading to the formation of the triple rings may be important in DNA condensation in vivo. 相似文献
159.
Georgy Milanovsky Oksana Gopta Anastasia Petrova Mahir Mamedov Michael Gorka Dmitry Cherepanov John H. Golbeck Alexey Semenov 《BBA》2019,1860(8):601-610
The kinetics of charge recombination in Photosystem I P700-FA/FB complexes and P700-FX cores lacking the terminal iron?sulfur clusters were studied over a temperatures range of 310 K to 4.2 K. Analysis of the charge recombination kinetics in this temperature range allowed the assignment of backward electron transfer from the different electron acceptors to P700+. The kinetic and thermodynamic parameters of these recombination reactions were determined. The kinetics of all electron transfer reactions were activation-less below 170 K, the glass transition temperature of the water-glycerol solution. Above this temperature, recombination from [FA/FB]? in P700-FA/FB complexes was found to proceed along two pathways with different activation energies (Ea). The charge recombination via A1A has an Ea of ~290 meV and is dominant at temperatures above ~280 K, whereas the direct recombination from FX? has an Ea of 22 meV and is prevalent in the 200 K to 270 K temperature range. Charge recombination from the FX cluster becomes highly heterogeneous at temperatures below 200 K. The conformational mobility of Photosystem I was studied by molecular dynamics simulations. The FX cluster was found to ‘swing’ by ~30° along the axis between the two sulfur atoms proximal to FA/FB. The partial rotation of FX is accompanied by significant changes of electric potential within the iron?sulfur cluster, which may induce preferential electron localization at different atoms of the FX cluster. These effects may account for the partial arrest of forward electron transfer and for the heterogeneity of charge recombination observed at the glass transition temperature. 相似文献
160.
A new method is proposed for the removal of the phenylhydrazide protecting group by the action of peroxidase or laccase, the enzymes attributed to the class of oxidoreductases. The deblocking procedure is performed under mild oxidative conditions, i.e., aqueous solution and neutral or close to neutral pH. Such mild oxidizing agents as 1 mM H(2)O(2) and air oxygen are used for unmasking. The method is available for the deblocking of both alpha- and gamma-carboxyl groups. The enzyme-catalyzed removal of the phenylhydrazide protecting group causes no oxidative modification nor destruction of methionine or tryptophan side chains. (c) 1993 John Wiley & Sons, Inc. 相似文献