Phosphate closes the solution structure of the 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) from Mycobacterium tuberculosis

The 5-enolpyruvylshikimate-3-phosphate synthase catalyses the sixth step of the shikimate pathway that is responsible for synthesizing aromatic compounds and is absent in mammals, which makes it a potential target for drugs development against microbial diseases. Here, we report the phosphate binding effects at the structure of the 5-enolpyruvyl shikimate-3-phosphate synthase from Mycobacterium tuberculosis. This enzyme is formed by two similar domains that close on each other induced by ligand binding, showing the occurrence of a large conformation change. We have monitored the phosphate binding effects using analytical ultracentrifugation, small angle X-ray scattering and, circular dichroism techniques. The low resolution results showed that the enzyme in the presence of phosphate clearly presented a more compact structure. Thermal-induced unfolding experiments followed by circular dichroism suggested that phosphate rigidified the enzyme. Summarizing, these data suggested that the phosphate itself is able to induce conformational change resulting in the closure movement in the M. tuberculosis 5-enolpyruvylshikimate-3-phosphate synthase. (c) 2006 Elsevier B.V. All rights reserved.

Ontogeny and Structure of the Pericarp of Schinus terebinthifolius Raddi (Anacardiaceae)

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Invasive Africanized honeybees change the structure of native pollination networks in Brazil

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Formation of wakes by chiral conducting cosmic strings

Chiral cosmic strings are naturally produced at the end of D-term inflation and they present very interesting cosmological consequences. In this work, we investigate the formation and evolution of wakes by a chiral string. We show that, for cold dark matter, the mechanism of forming wakes by a chiral string is similar to the mechanism by an ordinary string.

Structure of exotic three-body systems

The classification of large halos formed by two identical particles and a core is systematically addressed according to interparticle distances. The root-mean-square distances between the constituents are described by universal scaling functions obtained from a renormalized zero-range model. Applications for halo nuclei, Li-11 and Be-14, and for atomicn He-4(3) are briefly discussed. The generalization to four-body systems is proposed.

Binding and structure of tetramers in the scaling limit

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Effect of addition of MTES on the structure of siloxane-PPG nanocomposites

Hybrid transparent and flexible siloxane-polypropyleneglycol (PPG) materials with covalent bonds between the inorganic (siloxane) and organic (polymeric) phases were prepared by sol-gel process. In order to improve the quality of the mechanical properties of these materials, different amounts of methyltriethoxysilane (MTES) were added to the initial sol. The effect of MTES addition on the structure of the composites was studied by Small-Angle X-Ray Scattering (SAXS) and Si-29 Nuclear Magnetic Resonance (Si-29 NMR). In absence of MTES, SAXS spectra exhibit a peak that is assigned to spatial correlation due to short range order between the siloxane clusters embedded in the polymeric phase. The experimental results indicate that, for low MTES concentrations ([MTES]/[O] less than or equal to 0.8, O: ether-type oxygen of PPG), the silicon species resulting from hydrolysis and condensation of MTES fill the open spaces between polymeric chains, interacting with the ether-type oxygens. For larger MTES content ([MTES]/[O] greater than or equal to 0.8), the number of free ether-type oxygen sites avalaible for reaction with such silicon species is not large enough. Consequently, a fraction of silicon species resulting from MTES addition graft to siloxane clusters formed by hydrolysis and condensation of the hybrid precursor. For all MTES concentrations the condensation degree of the siloxane phase, determined from Si-29 NMR spectroscopy, is high (> 69%), as expected under neutral pH synthesis conditions.

Microhabitat and plant structure of Characeae (Chlorophyta) populations in streams from São Paulo State, southeastern Brazil

Microhabitat distribution was investigated in five populations of Characeae (two of Chara guairensis, two of Nitella subglomerata and one of Nitella sp.) to determine the distributional patterns, the morphometric and reproductive adaptations to varying environmental conditions and niche width on a scale of few centimeters. Variations in physical variables revealed some general trends of microhabitat distribution for the Characeae populations studied, with occurrence under the following conditions: slow and narrow current velocities; substrata predominantly composed of small particle size (sand-clay); variable and generally low depths. In terms of morphological adaptations, we found some general patterns: plants with longer whorl branchlets also had longer internodes in all populations studied, whereas longer plants had also thicker axis. The former were generally associated with higher biomass (percent cover). Few correlations of morphological characters were observed with environmental variables (e.g. plant length with irradiance: negative in two populations and positive in one population). Despite the general patterns of occurrence mentioned above, our results also indicated that each population differed in its responses to environmental variables and had particular morphological and reproductive adaptations. The Characean populations occurred under a narrower range of microhabitat conditions than other macroalgae from lotic habitats, particularly lower current velocity (6.7-9.8 cm s(-1)) and a more specific substratum type (sand-clay). Niche width values (0.60-0.99) of the Characeae populations studied indicate a high degree of habitat specialization and are among the highest yet found in lotic macroalgae. The relatively narrow variations in microhabitat conditions and high niche widths here reported for Characean populations, suggest a lower tolerance to variations in current velocity, depth, irradiance and substratum type. These characteristics probably explain the relatively restricted distribution of Characeae species in streams of S (a) over tildeo Paulo State with low frequency of records in most regions.

Self-assembled FePt nanocrystals with large coercivity: Reduction of the fcc-to-L1(0) ordering temperature

Herein we report the synthesis and properties of Fe55Pt45 nanoparticles, both monodisperse and self-assembled into hexagonal close-packed and cubic arrays of 4.0 +/- 0.2 nm size in an L1(0) structure, obtained by a modified polyol process. The new synthetic route improved the control over the particle composition, thereby reducing the temperature required to convert from face-centered cubic (fcc) to face-centered tetragonal (fct) phase by some 30-50 degrees C without additives. Annealing at 550 degrees C for 30 min converts the self-assembled nanoparticles into ferromagnetic nanocrystals with large coercivity, H-C = 11.1 kOe. Reducing the fcc-to-fct (L1(0)) ordering temperature avoided particle coalescence and decreased the loss in particle positional order without compromising the magnetic properties, as is generally observed when additives are used.

Local and nanoscopic structure of potassium triflate-doped siloxane-polyoxyethylene ormolytes

Siloxane-poly(oxyethylene) hybrids obtained by the sol-gel process and containing short polymer chain have been doped with potassium triflate (KCF3SO3). The local structure of these hybrids was investigated by X-ray absorption spectroscopy near the potassium K-edge. Small angle X-ray scattering was used to determine the structure at the nanometer scale. Results revealed that at low and medium potassium concentration (n = [O][K] >= 8, where n represents the molar ratio of ether-type oxygen atoms per alkaline cation) the cations interact mainly with the polymer chains, while at larger doping level (n < 8) the formation of a polyehter:KCF3SO3 Complex is observed. The nanoscopic structure of the hybrids is also affected by doping. By increasing the doping level, decreasing trends in the electronic density contrast between siloxane nanoparticles and polyether matrix and in the siloxane interparticle distance are observed. At high doping level the small angle X-ray scattering patterns are strongly modified, showing the disappearance of the correlation peak and the formation of a potassium-containing nanophase. (c) 2006 Elsevier B.V. All rights reserved.

Microhabitat and plant structure of Compsopogon coeruleus (Compsopogonaceae, Rhodophyta) populations in streams from São Paulo State, southeastern Brazil

Microhabitat distribution was investigated in three populations of C. coeruleus to determine the distributional patterns and their controlling factors, as well as morphometric adaptations to varying conditions on a scale of a few centimetres. Morphometric variations and their relations with physical variables (current velocity, irradiance, depth and type of substratum) revealed some particular characteristics for each population and indicate particular adaptations. However, some trends were clear: 1) larger plants (length and/or diameter) produced a higher quantity of monosporangia in the three populations; 2) plant length and diameter were positively correlated in two populations; 3) plant diameter was positively correlated with current velocity in two populations; 4) higher percent cover was associated with substrata composed of macrophytes in two populations. C. coeruleus occurred under relatively wide microhabitat conditions and had high niche width values, suggesting a tolerance to considerable variation in physical variables. These characteristics contribute to the species' wide distribution in Brazilian streams, both spatial (at distinct scales) and seasonal. (C) ADAC / Elsevier, Paris.

Optimum-Path Forest Classifier for Large Scale Biometric Applications

This paper addresses biometric identification using large databases, in particular, iris databases. In such applications, it is critical to have low response time, while maintaining an acceptable recognition rate. Thus, the trade-off between speed and accuracy must be evaluated for processing and recognition parts of an identification system. In this paper, a graph-based framework for pattern recognition, called Optimum-Path Forest (OPF), is utilized as a classifier in a pre-developed iris recognition system. The aim of this paper is to verify the effectiveness of OPF in the field of iris recognition, and its performance for various scale iris databases. The existing Gauss-Laguerre Wavelet based coding scheme is used for iris encoding. The performance of the OPF and two other - Hamming and Bayesian - classifiers, is compared using small, medium, and large-scale databases. Such a comparison shows that the OPF has faster response for large-scale databases, thus performing better than the more accurate, but slower, classifiers.

A Fast Large Scale Iris Database Classification with Optimum-Path Forest Technique: A Case Study

Majority of biometric researchers focus on the accuracy of matching using biometrics databases, including iris databases, while the scalability and speed issues have been neglected. In the applications such as identification in airports and borders, it is critical for the identification system to have low-time response. In this paper, a graph-based framework for pattern recognition, called Optimum-Path Forest (OPF), is utilized as a classifier in a pre-developed iris recognition system. The aim of this paper is to verify the effectiveness of OPF in the field of iris recognition, and its performance for various scale iris databases. This paper investigates several classifiers, which are widely used in iris recognition papers, and the response time along with accuracy. The existing Gauss-Laguerre Wavelet based iris coding scheme, which shows perfect discrimination with rotary Hamming distance classifier, is used for iris coding. The performance of classifiers is compared using small, medium, and large scale databases. Such comparison shows that OPF has faster response for large scale database, thus performing better than more accurate but slower Bayesian classifier.

Microhabitat and plant structure of Batrachospermum (Batrachospermales, Rhodophyta) populations in four streams of São Paulo State, southeastern Brazil

Microhabitat and plant structure of seven Batrachospermum populations (four of Batrachospermum delicatulum (= Sirodotia delicatula), one of Batrachospermum macrosporum and two of the 'Chantransia' stage), including the influence of physical variables (current velocity, depth, irradiance and substratum), were investigated in four streams of São Paulo State, southeastern Brazil. The populations of B. delicatulum and the 'Chantransia' stage occurred under very diverse microhabitat conditions, which probably contributes to their wide spatial and seasonal distribution in Brazilian streams. Results suggest branch reconfiguration as a probable mechanism of adaptation to current velocity based on the occurrence of: (i) B. macrosporum (a large mucilaginous form with presumably little ability for branch reconfiguration) under lower current velocity than B. delicatulum; (ii) only dense plants in populations with high current velocities (> 60 cm s-1), whereas 53-77% of dense plants were seen in populations exposed to lower currents (< 40 cm s-1); (iii) positive correlations of plant length with internode length in populations under low current velocities and negative correlation in a population with high velocity (132 cm s-1); and (iv) negative correlations of current velocity with plant diameter and internode length in a population under high flow. This study, involving mainly dioecious populations, revealed that B. delicatulum displayed higher fertilization rates than B. macrosporum. A complementary explanation for a dioecious species to increase fertilization success was proposed consisting of outcrossing among intermingled male and female adjacent plants within an algal spot.

The structure of waxy corn starch: Effect of granule size

The granules of waxy corn starch were isolated and various samples were separated by size and classified according to their average diameter in: non-separated granules (N), granules with diameter < 15 μm (S) and granules with diameter ≥ 15 μm (L). The samples were hydrolyzed by bacterial α-amylase and fungal amyloglucosidase. The starch granules remaining after enzymatic hydrolysis were analysed by X-ray diffraction and optical and scanning electron microscopy. Sephadex G-50 gel permeation chromatography of the dissolved residues from the hydrolysis of the N and S samples was performed directly and after successive enzymatic digestion with pullulanase and β-amylase. The results showed that the percentage of hydrolysis increased with a decrease in diameter. No apparent differences in waxy corn starch when observed under light and scanning electronic microscope were observed, regardless of diameter and enzyme action, although both large and small granules showed extensive surface corrosion after enzymatic attack. X-ray analysis suggested a decrease in the quantity of crystalline areas in the smaller granules, which would explain the high percentage of hydrolysis evidenced by these granules. The elution patterns of the α-glucans of both starches (N and S) were similar and reveled the presence of two fractions which were not susceptible to a-amylase and amyloglucosidase attack suggesting that these fractions were involved in the waxy corn starch crystalline regions. Debranching with pullulanase followed by gel-permeation chromatography showed that the amylopectins from the starch granules studied contained three groups of unit chains instead of the two reported in the literature.