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821.
The regulation of ATP synthase activity is complex and involves several distinct mechanisms. In bacteria and chloroplasts, subunit epsilon plays an important role in this regulation, (i) affecting the efficiency of coupling, (ii) influencing the catalytic pathway, and (iii) selectively inhibiting ATP hydrolysis activity. Several experimental studies indicate that the regulation is achieved through large conformational transitions of the alpha-helical C-terminal domain of subunit epsilon that occur in response to membrane energization, change in ATP/ADP ratio or addition of inhibitors. This review summarizes the experimental data obtained on different organisms that clarify some basic features as well as some molecular details of this regulatory mechanism. Multiple functions of subunit epsilon, its role in the difference between the catalytic pathways of ATP synthesis and hydrolysis and its influence on the inhibition of ATP hydrolysis by ADP are also discussed. 相似文献
822.
The role of carboxylic residues at the high-affinity, Mn-binding site in the ligation of iron cations blocking the site [Biochemistry 41 (2000) 5854] was studied, using a method developed to extract the iron cations blocking the site. We found that specifically bound Fe(III) cations can be extracted with citrate buffer at pH 3.0. Furthermore, citrate can also prevent the photooxidation of Fe(II) cations by YZ. Participation of a COOH group(s) in the ligation of Fe(III) at the high-affinity site was investigated using 1-ethyl-3-[(3-dimethylamino)propyl] carbodiimide (EDC), a chemical modifier of carboxylic amino acid residues. Modification of the COOH groups inhibits the light-induced oxidation of exogenous Mn(II) cations by Mn-depleted photosystem II (PSII[-Mn]) membranes. The rate of Mn(II) oxidation saturates at > or = 10 microM in PSII(-Mn) membranes and > or = 500 microM in EDC-treated PSII (-Mn) samples. Intact PSII(-Mn) membranes have only one site for Mn(II) oxidation via YZ (dissociation constant, Kd = 0.64 microM), while EDC-treated PSII(-Mn) samples have two sites (Kd = 1.52 and 22 microM; the latter is the low-affinity site). When PSII(-Mn) membranes were incubated with Fe(II) before modifier treatment (to block the high-affinity site) and the blocking iron cations were extracted with citrate (pH 3.0) after modification, the membranes contained only one site (Kd = 2.3 microM) for exogenous Mn(II) oxidation by Y(Z)() radical. In this case, the rate of electron donation via YZ saturated at a Mn(II) concentration > or = 15 microM. These results indicate that the carboxylic residue participating in Mn(II) coordination and the binding of oxidized manganese cations at the HAZ site is protected from the action of the modifier by the iron cations blocking the HAZ site. We concluded that the carboxylic residue (D1 Asp-170) participating in the coordination of the manganese cation at the HAZ site (Mn4 in the tetranuclear manganese cluster [Science 303 (2004) 1831]) is also involved in the ligation of the Fe cation(s) blocking the high-affinity Mn-binding site. 相似文献
823.
Boris R. Krasnov Michal Stanko Irina S. Khokhlova Ladislav Moanský Georgy I. Shenbrot Hadas Hawlena Serge Morand 《Ecography》2006,29(2):159-168
The aggregation model of coexistence states that species coexistence is facilitated if interspecific aggregation is reduced relative to intraspecific aggregation. We investigated the relationship between intraspecific and interspecific aggregation in 17 component communities (the flea assemblage of a host population) of fleas parasitic on small mammals and hypothesized that interspecific interactions should be reduced relative to intraspecific interactions, facilitating species coexistence. We predicted that the reduction of the level of interspecific aggregation in relation to the level of intraspecific aggregation would be positively correlated with total flea abundance and species richness of flea assemblages. We also expected that the higher degree of facilitation of flea coexistence would be affected by host parameters such as body mass, basal metabolic rate (BMR) and depth and complexity of burrows. Results of this study supported the aggregation model of coexistence and demonstrated that, in general, a) conspecific fleas were aggregated across their hosts; b) flea assemblages were not dominated by negative interspecific interactions; and c) the level of interspecific aggregation in flea assemblages was reduced in relation to the level of intraspecific aggregation. Intraspecific aggregation tended to be correlated positively to body mass, burrow complexity and mass-independent BMR of a host. Positive interspecific associations of fleas tended to occur more frequently in species-rich flea assemblages and/or in larger hosts possessing deep complex burrows. Intraspecific aggregation increased relative to interspecific aggregation when species richness of flea infracommunities (the flea assemblage of a host individual) and component communities increased. We conclude that the pattern of flea coexistence is related both to the structure of flea communities and affinities of host species. 相似文献
824.
825.
A one-step precipitation polymerization procedure for the synthesis of molecularly imprinted polymers selective for 17beta-estradiol yielding imprinted micro and nanospheres was developed in this study and compared to templated materials obtained by conventional bulk polymerization. The polymer particles prepared by precipitation polymerization exhibited a regular spherical shape at the micro and nanoscale with a high degree of monodispersity. Moreover, the influence of the polymerization temperature, and the ratio of functional monomer to cross-linker on the size of the obtained particles was investigated. The selectivity of the imprinted micro and nanospheres was evaluated by HPLC analysis and via radioligand binding assays. HPLC separation experiments revealed that the imprinted microspheres provide higher or similar affinity to the template in contrast to imprinted polymers prepared by conventional bulk polymerization or synthesized by multi-step swelling/polymerization methods. The dimensions of the imprinted nanospheres facilitate suspension in solution rendering them ideal for binding assay applications. Results from saturation and displacement assays prove that the imprinted nanospheres exhibit superior specific affinity to the target molecule in contrast to control materials. The binding properties of the nanospheres including binding isotherms and affinity distribution were studied via Freundlich isotherm affinity distribution (FIAD) analysis. Moreover, release experiments show that 70% of rebound 17beta-estradiol was released from the imprinted nanospheres within the first 2 h, while more intimately bound 17beta-estradiol molecules (approx. 16%) were released in the following 42 h. Fitting Brunnauer-Emmet-Teller (BET) multi-point adsorption isotherms to the obtained results indicated that the micro and nanospheres are characterized by a comparatively homogenous and narrow distribution of mesopores in contrast to the corresponding bulk polymers. 相似文献
826.
Gopalsamy A Shi M Ciszewski G Park K Ellingboe JW Orlowski M Feld B Howe AY 《Bioorganic & medicinal chemistry letters》2006,16(9):2532-2534
A novel class of HCV NS5B RNA dependent RNA polymerase inhibitors containing 2,3,4,9-tetrahydro-1H-carbazole and 1,2,3,4-tetrahydro-cyclopenta[b]indole scaffolds were designed and synthesized. Optimization of the aromatic region showed preference for 5,8-disubstitution pattern in both the scaffolds examined while favoring the n-propyl moiety for the C-1 position. 1,2,3,4-tetrahydro-cyclopenta[b]indole scaffold was slightly more potent than the corresponding 2,3,4,9-tetrahydro-1H-carbazole and analogue 36 displayed an IC50 of 550 nM against HCV NS5B enzyme. 相似文献
827.
Tadeusz Wroblewski Katherine S. Caldwell Urszula Piskurewicz Keri A. Cavanaugh Huaqin Xu Alexander Kozik Oswaldo Ochoa Leah K. McHale Kirsten Lahre Joanna Jelenska Jose A. Castillo Daniel Blumenthal Boris A. Vinatzer Jean T. Greenberg Richard W. Michelmore 《Plant physiology》2009,150(4):1733-1749
Bacterial plant pathogens manipulate their hosts by injection of numerous effector proteins into host cells via type III secretion systems. Recognition of these effectors by the host plant leads to the induction of a defense reaction that often culminates in a hypersensitive response manifested as cell death. Genes encoding effector proteins can be exchanged between different strains of bacteria via horizontal transfer, and often individual strains are capable of infecting multiple hosts. Host plant species express diverse repertoires of resistance proteins that mediate direct or indirect recognition of bacterial effectors. As a result, plants and their bacterial pathogens should be considered as two extensive coevolving groups rather than as individual host species coevolving with single pathovars. To dissect the complexity of this coevolution, we cloned 171 effector-encoding genes from several pathovars of Pseudomonas and Ralstonia. We used Agrobacterium tumefaciens-mediated transient assays to test the ability of each effector to induce a necrotic phenotype on 59 plant genotypes belonging to four plant families, including numerous diverse accessions of lettuce (Lactuca sativa) and tomato (Solanum lycopersicum). Known defense-inducing effectors (avirulence factors) and their homologs commonly induced extensive necrosis in many different plant species. Nonhost species reacted to multiple effector proteins from an individual pathovar more frequently and more intensely than host species. Both homologous and sequence-unrelated effectors could elicit necrosis in a similar spectrum of plants, suggesting common effector targets or targeting of the same pathways in the plant cell. 相似文献
828.
Boris R. Krasnov Maxim V. Vinarski Natalia P. Korallo-Vinarskaya David Mouillot Robert Poulin 《Oecologia》2009,160(1):175-185
Within a community, the abundance of any given species depends in large part on a network of direct and indirect, positive
and negative interactions with other species, including shared enemies. In communities where experimental manipulations are
often impossible (e.g., parasite communities), census data can be used to evaluate the strength or frequency of positive and
negative associations among species. In ectoparasite communities, competitive associations can arise because of limited space
or food, but facilitative associations can also exist if one species suppresses host immune defenses. In addition, positive
associations among parasites could arise merely due to shared preferences for the same host, without any interaction going
on. We used census data from 28 regional surveys of gamasid mites parasitic on small mammals throughout the Palaearctic, to
assess how the abundance of individual mite species is influenced by the abundance and diversity of other mite species on
the same host. After controlling for several confounding variables, the abundance of individual mite species was generally
positively correlated with the combined abundances of all other mite species in the community. This trend was confirmed by
meta-analysis of the results obtained for separate mite species. In contrast, there were generally no consistent relationships
between the abundance of individual mite species and either the species richness or taxonomic diversity of the community in
which they occur. These patterns were independent of mite feeding mode. Our results indicate either that synergistic facilitative
interactions among mites increase the host’s susceptibility to further attacks (e.g., via immunosuppression) and lead to different
species all having increased abundance on the same host, or that certain characteristics make some host species preferred
habitats for many parasite species.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
829.
Boris O. Schlumpberger Andrea A. Cocucci Marcela Mor�� Alicia N. S��rsic Robert A. Raguso 《Annals of botany》2009,103(9):1489-1500
Background and aims
A South American cactus species, Echinopsis ancistrophora (Cactaceae), with dramatic among-population variation in floral traits is presented.Methods
Eleven populations of E. ancistrophora were studied in their habitats in northern Argentina, and comparisons were made of relevant floral traits such as depth, stigma position, nectar volume and sugar concentration, and anthesis time. Diurnal and nocturnal pollinator assemblages were evaluated for populations with different floral trait combinations.Key Results
Remarkable geographical variations in floral traits were recorded among the 11 populations throughout the distribution range of E. ancistrophora, with flower lengths ranging from 4·5 to 24·1 cm. Other floral traits associated with pollinator attraction also varied in a population-specific manner, in concert with floral depth. Populations with the shortest flowers showed morning anthesis and those with the longest flowers opened at dusk, whereas those with flowers of intermediate length opened at unusual times (2300–0600 h). Nectar production varied non-linearly with floral length; it was absent to low (population means up to 15 µL) in short- to intermediate-length flowers, but was high (population means up to 170 µL) in the longest tubed flowers. Evidence from light-trapping of moths, pollen carriage on their bodies and moth scale deposition on stigmas suggests that sphingid pollination is prevalent only in the four populations with the longest flowers, in which floral morphological traits and nectar volumes match the classic expectations for the hawkmoth pollination syndrome. All other populations, with flowers 4·5–15 cm long, were pollinated exclusively by solitary bees.Conclusions
The results suggest incipient differentiation at the population level and local adaptation to either bee or hawkmoth (potentially plus bee) pollination.Key words: Pollination, floral biology, Echinopsis ancistrophora, cactus, Cactaceae, hawkmoth, bee 相似文献830.
Boris D. Zlatopolskiy Agnieszka Morgenroth Elizaveta A. Urusova Cornelia Dinger Thomas Kull Manuela Pape Gerhard Glatting Sven N. Reske 《Bioorganic & medicinal chemistry letters》2009,19(17):5151-5154
Three new potential hENT1 inhibitors suitable for labeling with PET/SPECT radioisotopes were prepared from an advanced intermediate 4. They were tested for their capability to inhibit binding of SAENTA-fluorescein to HL60 leukemia cells in flow cytometry assay and SAENTA-I (5) was determined to be the most active compound. 131I-5 showed high hENT1-specific binding (up to 54% ID) to 6 from 7 tested tumor cell lines and was chosen for further in vivo study. 相似文献