A covalently bound photoisomerizable agonist. Comparison with reversibly bound agonists at electrophorus electroplaques

After disulphide bonds are reduced with dithiothreitol, trans-3- (α-bromomethyl)-3’-[α- (trimethylammonium)methyl]azobenzene (trans-QBr) alkylates a sulfhydryl group on receptors. The membrane conductance induced by this “tethered agonist” shares many properties with that induced by reversible agonists. Equilibrium conductance increases as the membrane potential is made more negative; the voltage sensitivity resembles that seen with 50 [mu]M carbachol. Voltage- jump relaxations follow an exponential time-course; the rate constants are about twice as large as those seen with 50 μM carbachol and have the same voltage and temperature sensitivity. With reversible agonists, the rate of channel opening increases with the frequency of agonist-receptor collisions: with tethered trans-Qbr, this rate depends only on intramolecular events. In comparison to the conductance induced by reversible agonists, the QBr-induced conductance is at least 10-fold less sensitive to competitive blockade by tubocurarine and roughly as sensitive to “open-channel blockade” bu QX-222. Light-flash experiments with tethered QBr resemble those with the reversible photoisomerizable agonist, 3,3’,bis-[α-(trimethylammonium)methyl]azobenzene (Bis-Q): the conductance is increased by cis {arrow} trans photoisomerizations and decreased by trans {arrow} cis photoisomerizations. As with Bis-Q, ligh-flash relaxations have the same rate constant as voltage-jump relaxations. Receptors with tethered trans isomer. By comparing the agonist-induced conductance with the cis/tans ratio, we conclude that each channel’s activation is determined by the configuration of a single tethered QBr molecule. The QBr-induced conductance shows slow decreases (time constant, several hundred milliseconds), which can be partially reversed by flashes. The similarities suggest that the same rate-limiting step governs the opening and closing of channels for both reversible and tethered agonists. Therefore, this step is probably not the initial encounter between agonist and receptor molecules.     

Palatability and feeding preferences of Uresiphita maorialis (Lepidoptera: Crambidae) for three Sophora species

In a three-hour bioassay, we tested the palatability and feeding preferences of Uresiphita maorialis (kōwhai moth) for Sophora tetraptera, Sophora microphylla and Sophora prostrata. Palatability tests showed no differences among the Sophora species. Feeding preferences, on the other hand, showed that S. tetraptera and S. microphylla leaves are preferred over S. prostrata leaves. Our results support our field observations in Wellington city parks and gardens showing that S. tetraptera and S. microphylla plants frequently have higher densities of larvae than S. prostrata.     

Biodeterioration of Mayan buildings at uxmal and tulum,Mexico

Uxmal and Tulum are two important Mayan sites in the Yucatan peninsula. The buildings are mainly composed of limestone and grey/black discoloration is seen on exposed walls and copious greenish biofilms on inner walls. The principal microorganisms detected on interior walls at both Uxmal and Tulum were cyanobacteria; heterotrophic bacteria and filamentous fungi were also present. A dark‐pigmented mitosporic fungus and Bacillus cereus, both isolated from Uxmal, were shown to be acidogenic in laboratory cultures. Cyanobacteria belonging to rock‐degrading genera Synechocystis and Gloeocapsa were identified at both sites. Surface analysis previously showed that calcium ions were present in the biofilms on buildings at Uxmal and Tulum, suggesting the deposition of biosolubilized stone. Apart from their potential to degrade the substrate, the coccoid cyanobacteria supply organic nutrients for bacteria and fungi, which can produce organic acids, further increasing stone degradation.     

The role of fish-poultry integration on fish growth performance,yields and economic benefits among smallholder farmers in sub-Saharan Africa,Tanzania

Aquaculture practices from sub-Saharan Africa are characterised by low production, owing to improper technology. Production can be increased through integrating fish farming with other existing on-farm activities, particularly livestock husbandry. We assessed the role of fish-poultry integration on all male Nile tilapia, Oreochromis niloticus growth performance, yields and economic benefits among smallholder farmers in sub-Saharan Africa, Tanzania. The study also compared phytoplankton species composition, abundance and biomass between the fish-poultry integration and non-integrated system. After 180 days of the experiment, all male O. niloticus cultured under fish-poultry integration exhibited significantly higher growth rates than those in the non-integrated system (p < 0.05). Gross fish yield (GFY), net fish yield (NFY) and net annual yields (NAY) obtained from fish-poultry integration were significantly higher than those from non-integrated system (p < 0.05). Partial enterprise budget analysis revealed that fish-poultry integration was more profitable than the non-integrated system. Moreover, fish-poultry integrated system produced significantly higher phytoplankton abundance and biomass than those from the non-integrated system. Results demonstrate that rural smallholder farmers can achieve higher growth rate, farm net yields and income by integrating all male O. niloticus with other on-farm activities than practising a stand-alone fish culture system.     

Characterization of two partially unfolded intermediates of the molecular chaperone DnaK at low pH

In this study, the effect of pH on the conformation and the reactivity of the Escherichia coli Hsp70 molecular chaperone DnaK was investigated using spectroscopic and chemical assays. DnaK exhibits negligible binding of the hydrophobic dye 1-anilino-naphthalene-8-sulfonate (ANS) between pH 7 to 5.0, whereas appreciable binding occurs between pH 4.5 to 4.0. The binding of ANS to a protein is diagnostic of the presence of accessible ordered hydrophobic surfaces. Such hydrophobic surfaces are often displayed by partially folded protein intermediates such as molten globules. Nucleotide inhibits 70% of the ANS binding at pH 4.5 but none of the ANS binding at pH 4.0. Proteolysis of nucleotide-free DnaK at pH 4.5 with cathepsin D yields detectable fragments (masses > 20 kDa) of the C-terminal peptide-binding domain but none of the N-terminal ATPase domain, thus the ATPase domain is preferentially targeted for proteolysis. In contrast, proteolysis of nucleotide-free DnaK at pH 4.0 with cathepsin D cuts near the linker region, yielding both functional domains. Our interpretation of these data is that incubation of DnaK at pH 4.5 produces a partially unfolded form of the ATPase domain, in which secondary structure is mainly intact, but tertiary structure is reduced. Incubation of the protein at pH 4.0 produces an intermediate in which both functional domains have collapsed and possibly separated. Nucleotide inhibits the conformational change that occurs at pH 4.5 but not at 4.0.     

Roles of ATP binding and ATP hydrolysis in human Rad51 recombinase function

The Rad51 recombinase polymerizes on ssDNA to yield a right-handed nucleoprotein filament, called the presynaptic filament, that can search for homology in duplex DNA and pair the recombining DNA molecules to form a DNA joint. ATP is needed for presynaptic filament assembly and homologous DNA pairing, but the roles of ATP binding and ATP hydrolysis in the overall reaction scheme have not yet been clearly defined. To address this issue, we have constructed two mutants of hRad51, hRad51 K133A and hRad51 K133R, expressed these mutant variants in Escherichia coli, and purified them to near homogeneity. Both hRad51 mutant variants are greatly attenuated for ATPase activity, but hRad51 K133R retains the ability to protect DNA from restriction enzyme digest and induce topological changes in duplex DNA in an ATP-dependent manner, whereas the hRad51 K133A variant is inactive. With biochemical means, we show that the presynaptic filament becomes greatly stabilized when ATP hydrolysis is prevented, leading to an enhanced ability of the presynaptic filament to catalyze homologous pairing. These results help form the basis for understanding the functions of ATP binding and ATP hydrolysis in hRad51-mediated recombination reactions.     

The many faces of ubiquitinated histone H2A: insights from the DUBs

Increasing knowledge on the cell cycle deregulations in cancers has promoted the introduction of phytochemicals, which can either modulate signaling pathways leading to cell cycle regulation or directly alter cell cycle regulatory molecules, in cancer therapy. Most human malignancies are driven by chromosomal translocations or other genetic alterations that directly affect the function of critical cell cycle proteins such as cyclins as well as tumor suppressors, e.g., p53. In this respect, cell cycle regulation and its modulation by curcumin are gaining widespread attention in recent years. Extensive research has addressed the chemotherapeutic potential of curcumin (diferuloylmethane), a relatively non-toxic plant derived polyphenol. The mechanisms implicated are diverse and appear to involve a combination of cell signaling pathways at multiple levels. In the present review we discuss how alterations in the cell cycle control contribute to the malignant transformation and provide an overview of how curcumin targets cell cycle regulatory molecules to assert anti-proliferative and/or apoptotic effects in cancer cells. The purpose of the current article is to present an appraisal of the current level of knowledge regarding the potential of curcumin as an agent for the chemoprevention of cancer via an understanding of its mechanism of action at the level of cell cycle regulation. Taken together, this review seeks to summarize the unique properties of curcumin that may be exploited for successful clinical cancer prevention.     

苹果园光能截获率的数学模型

应用气象学原理推导了不同纬度、不同栽植行向、不同树形的苹果园光能截获率的数学模型,给出在保证树冠基部外围日照时间大于25％总日照时间的条件下,生长季中充分截获光能的最佳树形、行距、冠高、冠径的优化组合方案。实例分析表明,计算结果与专家经验基本一致。本研究为果园合理栽植,充分利用光能,合理整形修剪提供理论依据与参考方案。