An interplanetary mission to Neptune system: Gravitational capture and maneuvers around triton

The gravitational capture was initially used to understand the capture of planetary satellites. However, in the 90's decade, this phenomenon was applied in spacecraft trajectories. Belbruno and Miller studied missions in the Earth-Moon system that uses this technique to save fuel during the insertion of the spacecraft in its final orbit around the Moon. Using a parameter defined as twice the two-body energy of the planet-particle system, Yamakawa also studied the gravitational capture in the Earth-Moon system. In the present paper, this technique is used to study a mission that goes to the Neptune system and perform a gravitational capture in the satellite Triton. The results show direct and retrograde trajectories, for different values of the initial conditions.

Public-private partnerships in renewable energy in Latin America and the Caribbean

Incluye Bibliografía

Purification, characterization, and specificity determination of a new serine protease secreted by penicillium waksmanii

The purpose of this work was to purify a protease from Penicillium waksmanii and to determine its biochemical characteristics and specificity. The extracellular protease isolated that was produced by P. waksmanii is a serine protease that is essential for the reproduction and growth of the fungus. The protease isolated showed 32 kDa, and has optimal activity at pH 8.0 and 35 C towards the substrate Abz-KLRSSKQ-EDDnp. The protease is active in the presence of CaCl2, KCl, and BaCl, and partially inhibited by CuCl2, CoCl2 and totally inhibited by AlCl3 and LiCl. In the presence of 1 M urea, the protease remains 50 % active. The activity of the protease increases 60 % when it is exposed to 0.4 % nonionic surfactant-Triton X-100 and loses 10 % activity in the presence of 0.4 % Tween-80. Using fluorescence resonance energy transfer analysis, the protease showed the most specificity for the peptide Abz-KIRSSKQ-EDDnp with k cat/K m of 10,666 mM-1 s-1, followed by the peptide Abz-GLRSSKQ-EDDnp with a k cat/K m of 7,500 mM -1 s-1. Basic and acidic side chain-containing amino acids performed best at subsite S1. Subsites S2, S3, S′ 2, and S′ 1, S ′ 3 showed a preference for binding for amino acids with hydrophobic and basic amino acid side chain, respectively. High values of k cat/K m were observed for the subsites S2, S3, and S′ 2. The sequence of the N-terminus (ANVVQSNVPSWGLARLSSKKTGTTDYTYD) showed high similarity to the fungi Penicillium citrinum and Penicillium chrysogenum, with 89 % of identity at the amino acid level. © 2012 Springer Science+Business Media New York.

Binding of antioxidant flavone isovitexin to human serum albumin investigated by experimental and computational assays

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Finite-difference calculation of donor energy levels in a spherical quantum dot subject to a magnetic field

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Interaction of cationic water-soluble meso-tetrakis(4-N-methylpyridiniumyl)porphyrin (TMPyP) with ionic and nonionic micelles: aggregation and binding

The equilibrium of meso-tetrakis(4-N-methylpyridiniumyl)porphyrin (TMPyP) in aqueous solution in the presence of surfactants was studied by optical spectroscopic techniques and SAXS (small angle X-ray scattering). Anionic SDS (sodium dodecyl sulfate), zwitterionic HPS (N-hexadecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate) and nonionic TRITON X-100 (t-octyl-phenoxypolyethoxyethanol), surfactants were used. TMPyP is characterized by a protonation equilibrium with a pK(a) around 1.0, associated with the diacid-free base transition, and a second pK(a) around 12.0 related with the transition between the free base and the monoanion form. Three independent species were observed for TMPyP at pH 6.0 as a function of SDS concentration: free TMPyP, TMPyP-SDS aggregates and porphyrin monomer bound to micelles. For HPS and TRITON X-100, the equilibrium of TMPyP as a function of pH is quite similar to that obtained in pure aqueous solution: no aggregation was observed, suggesting that electrostatic contribution is the major factor in the interaction between TMPyP and surfactants. SAXS data analysis demonstrated a prolate ellipsoidal shape for SDS micelles; no significant changes in shape and size were observed for SDS-TMPyP co-micelles. Moreover, the ionization coefficient, alpha, decreases with the increase of the porphyrin concentration, suggesting the ""screening"" of the anionic charge of SDS by the cationic porphyrin. These results are consistent with optical absorption, fluorescence and RLS (resonance light scattering) spectroscopies data, allowing to conclude that neutral surfactants present a smaller interaction with the cationic porphyrin as compared with an ionic surfactant. Therefore, the interaction of TMPyP with the ionic and nonionic surfactants is predominantly due to the electrostatic contribution. Copyright (c) 2008 Society of Porphyrins & Phthalocyanines.

Paper-based diffusive gradients in thin films technique coupled to energy dispersive X-ray fluorescence spectrometry for the determination of labile Mn, Co, Ni, Cu, Zn and Pb in river water

The diffusive gradients in thin films (DGT) technique has shown enormous potential for labile metal monitoring in fresh water due to the preconcentration, time-integrated, matrix interference removal and speciation analytical features. In this work, the coupling of energy dispersive X-ray fluorescence (EDXRF) with paper-based DGT devices was evaluated for the direct determination of Mn, Co. Ni, Cu, Zn and Pb in fresh water. The DGT samplers were assembled with cellulose (Whatman 3 MM chromatography paper) as the diffusion layer and a cellulose phosphate ion exchange membrane (Whatman P 81 paper) as the binding agent. The diffusion coefficients of the analytes on 3 MM chromatography paper were calculated by deploying the DGT samplers in synthetic solutions containing 500 mu g L-1 of Mn. Co, Ni, Cu, Zn and Pb (4 L at pH 5.5 and ionic strength at 0.05 mol L-1). After retrieval, the DGT units were disassembled and the P81 papers were dried and analysed by EDXRF directly. The 3 MM chromatographic paper diffusion coefficients of the analytes ranged from 1.67 to 1.87 x 10(-6) cm(2) s(-1). The metal retention and phosphate group homogeneities on the P81 membrane was studied by a spot analysis with a diameter of 1 mm. The proposed approach (DGT-EDXRF coupling) was applied to determine the analytes at five sampling sites (48 h in situ deployment) on the Piracicaba river basin, and the results (labile fraction) were compared with 0.45 mu m dissolved fractions determined by synchrotron radiation-excited total reflection X-ray fluorescence (SR-TXRF). The limits of detection of DGT-EDXRF coupling for the analytes (from 7.5 to 26 mu g L-1) were similar to those obtained by the sensitive SR-TXRF technique (3.8 to 9.1 mu g L-1). (C) 2012 Elsevier B.V. All rights reserved.

Supersymmetric Isospectral Formalism for the Calculation of Near-Zero Energy States: Application to the Very Weakly Bound He-4 Trimer Excited State

We propose a novel mathematical approach for the calculation of near-zero energy states by solving potentials which are isospectral with the original one. For any potential, families of strictly isospectral potentials (with very different shape) having desirable and adjustable features are generated by supersymmetric isospectral formalism. The near-zero energy Efimov state in the original potential is effectively trapped in the deep well of the isospectral family and facilitates more accurate calculation of the Efimov state. Application to the first excited state in He-4 trimer is presented.

Characterization of suramin binding sites on the human group IIA secreted phospholipase A(2) by site-directed mutagenesis and molecular dynamics simulation

Suramin is a polysulphonated naphthylurea with inhibitory activity against the human secreted group IIA phospholipase A(2) (hsPLA2GIIA), and we have investigated suramin binding to recombinant hsPLA2GIIA using site-directed mutagenesis and molecular dynamics (MD) simulations. The changes in suramin binding affinity of 13 cationic residue mutants of the hsPLA2GIIA was strongly correlated with alterations in the inhibition of membrane damaging activity of the protein. Suramin binding to hsPLA2GIIA was also studied by MD simulations, which demonstrated that altered intermolecular potential energy of the suramin/mutant complexes was a reliable indicator of affinity change. Although residues in the C-terminal region play a major role in the stabilization of the hsPLA2GIIA/suramin complex, attractive and repulsive hydrophobic and electrostatic interactions with residues throughout the protein together with the adoption of a bent suramin conformation, all contribute to the stability of the complex. Analysis of the h5PLA2GIIA/suramin interactions allows the prediction of the properties of suramin analogues with improved binding and higher affinities which may be candidates for novel phospholipase A(2) inhibitors. (C) 2012 Elsevier Inc. All rights reserved.

Dual-energy multidetector CT: how does it work, what can it tell us, and when can we use it in abdominopelvic imaging?

Dual-energy CT provides information about how substances behave at different energies, the ability to generate virtual unenhanced datasets, and improved detection of iodine-containing substances on low-energy images. Knowing how a substance behaves at two different energies can provide information about tissue composition beyond that obtainable with single-energy techniques. The term K edge refers to the spike in attenuation that occurs at energy levels just greater than that of the K-shell binding because of the increased photoelectric absorption at these energy levels. K-edge values vary for each element, and they increase as the atomic number increases. The energy dependence of the photoelectric effect and the variability of K edges form the basis of dual-energy techniques, which may be used to detect substances such as iodine, calcium, and uric acid crystals. The closer the energy level used in imaging is to the K edge of a substance such as iodine, the more the substance attenuates. In the abdomen and pelvis, dual-energy CT may be used in the liver to increase conspicuity of hypervascular lesions; in the kidneys, to distinguish hyperattenuating cysts from enhancing renal masses and to characterize renal stone composition; in the adrenal glands, to characterize adrenal nodules; and in the pancreas, to differentiate between normal and abnormal parenchyma.

Endocrine changes and liver mRNA abundance of somatotropic axis and insulin system constituents during negative energy balance at different stages of lactation in dairy cows

The liver has an important role in metabolic regulation and control of the somatotropic axis to adapt successfully to physiological and environmental changes in dairy cows. The aim of this study was to investigate the adaptation to negative energy balance (NEB) at parturition and to a deliberately induced NEB by feed restriction at 100 days in milk. The hepatic gene expression and the endocrine system of the somatotropic axis and related parameters were compared between the early and late NEB period. Fifty multiparous cows were subjected to 3 periods (1=early lactation up to 12 wk postpartum, 2=feed restriction for 3 wk beginning at around 100 days in milk with a feed-restricted and a control group, and 3=subsequent realimentation period for the feed-restricted group for 8 wk). In period 1, plasma growth hormone reached a maximum in early lactation, whereas insulin-like growth factor-I (IGF-I), leptin, the thyroid hormones, insulin, and the revised quantitative insulin sensitivity check index increased gradually after a nadir in early lactation. Three days after parturition, hepatic mRNA abundance of growth hormone receptor 1A, IGF-I, IGF-I receptor and IGF-binding protein-3 (IGFBP-3) were decreased, whereas mRNA of IGFBP-1 and -2 and insulin receptor were upregulated as compared with wk 3 antepartum. During period 2, feed-restricted cows showed decreased plasma concentrations of IGF-I and leptin compared with those of control cows. The revised quantitative insulin sensitivity check index was lower for feed-restricted cows (period 2) than for control cows. Compared with the NEB in period 1, the changes due to the deliberately induced NEB (period 2) in hormones were less pronounced. At the end of the 3-wk feed restriction, the mRNA abundance of IGF-I, IGFBP-1, -2, -3, and insulin receptor was increased as compared with the control group. The different effects of energy deficiency at the 2 stages in lactation show that the endocrine regulation changes qualitatively and quantitatively during the course of lactation.

A time-resolved fluorescence resonance energy transfer assay suitable for high-throughput screening for inhibitors of immunoglobulin E-receptor interactions

The interaction of immunoglobulin E (IgE) antibodies with the high-affinity receptor, FcεRI, plays a central role in initiating most allergic reactions. The IgE-receptor interaction has been targeted for treatment of allergic diseases, and many high-affinity macromolecular inhibitors have been identified. Small molecule inhibitors would offer significant advantages over current anti-IgE treatment, but no candidate compounds have been identified and fully validated. Here, we report the development of a time-resolved fluorescence resonance energy transfer (TR-FRET) assay for monitoring the IgE-receptor interaction. The TR-FRET assay measures an increase in fluorescence intensity as a donor lanthanide fluorophore is recruited into complexes of site-specific Alexa Fluor 488-labeled IgE-Fc and His-tagged FcεRIα proteins. The assay can readily monitor classic competitive inhibitors that bind either IgE-Fc or FcεRIα in equilibrium competition binding experiments. Furthermore, the TR-FRET assay can also be used to follow the kinetics of IgE-Fc-FcεRIα dissociation and identify inhibitory ligands that accelerate the dissociation of preformed complexes, as demonstrated for an engineered DARPin (designed ankyrin repeat protein) inhibitor. The TR-FRET assay is suitable for high-throughput screening (HTS), as shown by performing a pilot screen of the National Institutes of Health (NIH) Clinical Collection Library in a 384-well plate format.

Substrate binding tunes conformational flexibility and kinetic stability of an amino acid antiporter

We used single molecule dynamic force spectroscopy to unfold individual serine/threonine antiporters SteT from Bacillus subtilis. The unfolding force patterns revealed interactions and energy barriers that stabilized structural segments of SteT. Substrate binding did not establish strong localized interactions but appeared to be facilitated by the formation of weak interactions with several structural segments. Upon substrate binding, all energy barriers of the antiporter changed thereby describing the transition from brittle mechanical properties of SteT in the unbound state to structurally flexible conformations in the substrate-bound state. The lifetime of the unbound state was much shorter than that of the substrate-bound state. This leads to the conclusion that the unbound state of SteT shows a reduced conformational flexibility to facilitate specific substrate binding and a reduced kinetic stability to enable rapid switching to the bound state. In contrast, the bound state of SteT showed an increased conformational flexibility and kinetic stability such as required to enable transport of substrate across the cell membrane. This result supports the working model of antiporters in which alternate substrate access from one to the other membrane surface occurs in the substrate-bound state.

Different adaptation of IGF-I and its IGFBPs in dairy cows during a negative energy balance in early lactation and a negative energy balance induced by feed restriction in mid-lactation

Control of metabolic pathways is a major task of the somatotropic axis and its constituents. Insulinlike growth-factor binding proteins (IGFBPs) bind IGF-I and -II and act as carriers and regulators of their activities in blood, body fluids and tissues. Over two periods of physiological adaptation, this study investigated the binding pattern of IGF-I to IGFBPs in the plasma of 50 multiparous Holstein dairy cows and identified relationships with the hepatic mRNA abundance of IGFBPs and plasma IGF-I during the lactational negative energy balance (NEB) and during a deliberately induced NEB by feed restriction. Period 1 lasted from week 3 antepartum (a.p.) to week 12 postpartum (p.p.) and period 2, the period of feed restriction, started at around 100 DIM and lasted for three weeks with a control (C) and a restricted group (R). Blood samples and liver biopsies were collected in week 3 a.p., and in weeks 1 and 4 p.p. of period 1 and in weeks 0 and 3 of period 2. For column chromatography of IGFBPs, plasma samples of all animals were pooled by group and time points of sampling. Plasma IGF-I dropped from week 3 a.p. to week 1 p.p. and thereafter increased until week 0 (period 2) and did not change up to week 3 of period 2. The binding of IGF-I to plasma IGFBP-1 and -2 increased in period 1 from week 3 a.p. to week 4 p.p., while at the same time it decreased for IGFBP-3. During period 2, the binding of IGF-I to plasma IGFBP-1 and -2 decreased for both groups, but less for R cows. In C cows, the IGF-I binding to IGFBP-3 in plasma increased from week 0 to week 3 of period 2, whereas R cows showed a slight decrease. In period 1, hepatic mRNA abundance of IGFBP-3 followed the plasma IGFBP-3 binding in contrast to the mRNA abundances of IGFBP-1 and -2. The latter increased from week 3 a.p. to week 1 p.p. and decreased afterwards whereas IGF-I binding to IGFBP-1 and -2 increased. In week 3 of period 2, the binding of IGF-I to IGFBP-1 and -2 and their hepatic mRNA abundance were higher in R cows compared to C cows. Hepatic mRNA abundance of IGF-I was consistently positively correlated with plasma IGF-I, especially pronounced during the NEBs in week 1 p.p. (period 1) and in week 3 (period 2) in R cows. While no distinct relation between mRNA abundance of IGFBP-1 and plasma IGF-I was evident, the mRNA abundance of IGFBP-2 was inversely related to plasma IGF-I over all experimental time points independent of treatment. The mRNA abundance of IGFBP-3 was particularly correlated with plasma IGF-I during the 2 experimental stages of a NEB. Obviously IGFBP-3, but not IGFBP-1 and -2, binding in plasma closely followed the respective pattern of hepatic mRNA abundance during the entire experimental period. The fact that changes in the different plasma IGFBPs during altering metabolic stages in different stages of lactation do not always strictly follow their mRNA abundance in liver suggests tissues other than the liver flexibly contributing to the IGFBP pool in plasma as well as a partially post-transcriptional regulation of IGFBP synthesis.

AMPA RECEPTOR ALLOSTERISM: MEASUREMENT OF THE CONFORMATIONAL CHANGES IN THE LIGAND BINDING DOMAIN OF A FUNCTIONAL RECEPTOR

Ionotropic glutamate receptors are important excitatory neurotransmitter receptors in the mammalian central nervous system that have been implicated in a number of neuropathologies such as epilepsy, ischemia, and amyotrophic lateral sclerosis. Glutamate binding to an extracellular ligand binding domain initiates a series of structural changes that leads to the formation of a cation selective transmembrane channel, which consequently closes due to desensitization of the receptor. The crystal structures of the AMPA subtype of the glutamate receptor have been particularly useful in providing initial insight into the conformational changes in the ligand binding domain; however, these structures are limited by crystallographic constraint. To gain a clear picture of how agonist binding is coupled to channel activation and desensitization, it is essential to study changes in the ligand binding domain in a dynamic, physiological state. In this dissertation, a technique called Luminescence Resonance Energy Transfer was used to determine the conformational changes associated with activation and desensitization in a functional AMPA receptor (ÄN*-AMPA) that contains the ligand binding domain and transmembrane segments; ÄN*-AMPA has been modified such that fluorophores can be introduced at specific sites to serve as a readout of cleft closure or to establish intersubunit distances. Previous structural studies of cleft closure of the isolated ligand binding domain in conjunction with functional studies of the full receptor suggest that extent of cleft closure correlates with extent of activation. Here, LRET has been used to show that a similar relationship between cleft closure and activation is observed in the “full length” receptor showing that the isolated ligand binding domain is a good model of the domain in the full length receptor for changes within a subunit. Similar LRET investigations were used to study intersubunit distances specifically to probe conformational changes between subunits within a dimer in the tetrameric receptor. These studies show that the dimer interface is coupled in the open state, and decoupled in the desensitized state, similar to the isolated ligand binding domain crystal structure studies. However, we show that the apo state dimer interface is not pre-formed as in the crystal structure, hence suggesting a mechanism for functional transitions within the receptor based on LRET distances obtained.