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A novel nanocomposite of CdTe-PAMAM-MWNT was synthesized by covalently linking CdTe quantum dots (QDs) onto highly water-soluble multi-wall carbon nanotubes (MWNTs) functionalized with dendritic poly(amidoamine) (PAMAM). The IR, UV-vis and TEM methods has been used for the characterization of the composites. A facile method for controlling the density of QDs in the composite by simply changing the ratio of CdTe QDs/PAMAM-MWNT, as was verified by the TEM images. The experiments revealed that PAMAM and PAMAM-MWNT, once covalently linked with CdTe QDs, had remarkable effect on their fluorescence property. The fluorescence intensity of the CdTe-PAMAM hybrid was substantially enhanced as a compared to that of QDs, and the fluorescence was quenched greatly when QDs reacted with PAMAM-MWNT. The experimentally observed phenomena indicate that electron and energy transfer took place efficiently between CdTe QDs, PAMAM and MWNTs in the novel composite. These nanocomposits might hold great potential in photoelectron device and biotechnology applications.
Spectrochim Acta A Mol Biomol Spectrosc 2008 Oct
PMID:A novel density-tunable nanocomposites of CdTe quantum dots linked to dendrimer-tethered multi-wall carbon nanotubes. 1802 7

Photoluminescent nanoparticles of gold with size 3, 4, 6, and 9 nm are prepared by borohydride/citrate reduction in presence of polyethylene glycol (PEG)/tannic acid. The prepared nanomaterials are characterized by UV-vis spectroscopy and dynamic light scattering (DLS) technique. Intense photoluminescence (PL) is observed in nanoparticles prepared by fast reduction with borohydride in presence of PEG. A red shift of PL emission from 408 to 456 nm is observed for the change of size from 4 to 6 nm. Increase in PL intensity is observed for all the nanoparticles on the addition of KCl. Citrate reduced gold colloid which consists of large particles of size approximately 35 nm with anisotropic shapes showing two plasmon peaks is also prepared. The anisotropy is confirmed by TEM measurement. SERS activity of this colloid is tested using glutamic acid as an adsorbate probe. Assignment of the observed bands is given.
Spectrochim Acta A Mol Biomol Spectrosc 2008 Nov 01
PMID:Synthesis and spectroscopic characterization of gold nanoparticles. 1815 56

Silver nanoparticles of different sizes were prepared by citrate reduction and characterized by UV-vis absorbance spectra, TEM images and photoluminescence spectra. The morphology of the colloids obtained consists of a mixture of nanorods and spheres. The surface plasmon resonance (SPR) and photoemission properties of Ag nanoparticles are found to be sensitive to citrate concentration. A blue shift in SPR and an enhancement in photoluminescence intensity are observed with increase in citrate concentration. Effect of addition of KCl and variation of pH in photoluminescence was also studied.
Spectrochim Acta A Mol Biomol Spectrosc 2008 Nov 01
PMID:Studies on surface plasmon resonance and photoluminescence of silver nanoparticles. 1822 6

Electron microscopy of bacterial pathogens and interactions between bacteria and host cells and tissues provides valuable insights into structural and molecular properties and processes involved in pathogenesis. Applications for electron microscopy in bacterial pathogenesis range from discovering etiologic agents and following chronological events during infections by conventional examination of clinical samples to assessing molecular host-cell responses to infection and in situ interactions between receptors and ligands using specific immune-labeling techniques. This chapter focuses on techniques for preparing samples of bacteria and host cells for conventional transmission (TEM) and scanning electron microscopy (SEM) and use of luminescent nanocrystals or "quantum dots" as specific probes for correlative light and electron microscopy. Conventional TEM and SEM are well established tools for high resolution examination of structural effects and chronological events associated with bacterial infections. The recent development of quantum dots as physiological and immunological probes in biology has provided a powerful technique for bridging fluorescent analyses of fixed and live material with preparation and examination by TEM and SEM.
Methods Mol Biol 2008
PMID:Ultrastructural analysis of bacteria-host cell interactions. 1828 56

What changes occur when a natural protein that had been under low mutation rates is subjected to a neutral drift at high mutational loads, thus generating genetically diverse (polymorphic) gene ensembles that all maintain the protein's original function and structure? To address this question we subjected large populations of TEM-1 beta-lactamase to a prolonged neutral drift, applying high mutation rates and purifying selection to maintain TEM-1's existing penicillinase activity. Purging of deleterious mutations and enrichment of beneficial ones maintained the sequence of these ensembles closer to TEM-1's family consensus and inferred ancestor. In particular, back-to-consensus/ancestor mutations that increase TEM-1's kinetic and thermodynamic stability were enriched. These acted as global suppressors and enabled the tolerance of a broad range of deleterious mutations, thus further increasing the genetic diversity of the drifting populations. The probability of a new function emerging (cefotaxime degradation) was also substantially increased in these ensembles owing to the presence of many gene variants carrying the global suppressors. Our findings indicate the unique features of large, polymorphic neutral ensembles generated under high mutational loads and prompt the speculation that the progenitors of today's proteins may have evolved under high mutational loads. The results also suggest that predictable back-to-consensus/ancestor changes can be used in the laboratory to generate highly diverse and evolvable gene libraries.
J Mol Biol 2008 Jun 20
PMID:Intense neutral drifts yield robust and evolvable consensus proteins. 1849 57

Dimerization and antioxidant activity of morin in the Triton X-100 micelles were studied by electronic absorption, ATR-FTIR spectra, cyclic voltammetric, DSC, freeze-fracture TEM, molecular modeling and ab initio quantum calculations. Morin can be solubilized in the Triton X-100 micelles and show selective dimerization in Triton X-100 micelles with different structures. In Triton X-100 spherical micelles, morin always exists in the form of dimer, and in Triton X-100 rodlike micelles, it is always in the form of monomer. The solubilization of morin dimer in Triton X-100 spherical micelles changes the micelle morphology from spherical to cubelike, and the size of the single micelle is also increased, while morin monomer links the Triton X-100 rodlike micelles and forms a kind of network micelle structure with the size of the "rod" unchanged. Solubilized and concentrated in Triton X-100 micelles, morin can protect human serum albumin from the damage induced by hydroxyl radicals effectively and even can form a kind of protein complex with human serum albumin showing more thermal stability.
Mol Pharm
PMID:Effects of Triton X-100 nanoaggregates on dimerization and antioxidant activity of morin. 1851 Mar 37

Nanoparticles of CdS were prepared at 303 K by aqueous precipitation method using CdSO4 and (NH4)2S in presence of the stabilizing agent thioglycerol. Adjustment of the thioglycerol (T) to ammonium sulphide (A) ratio (T:A) from 1:25 to 1:3.3 was done during synthesis and nanoparticles of different size were obtained. The prepared colloids were characterized by UV-vis and photoluminescence (PL) spectroscopic studies. Prominent first and second excitonic transitions are observed in the UV-vis spectrum of the colloid prepared with a T:A ratio of 1:3.3. Particle size analysis was done using XRD, high resolution TEM and dynamic light scattering and found to be approximately 3 nm. UV-vis and PL spectral features also agree with this particle size in colloid with T:A of 1:3.3. The band gap of CdS quantum dots has increased from the bulk value 2.4-2.9 eV. PL spectra show quantum size effect and the peak is shifted from 628 to 556 nm when the ratio of T:A was changed from 1:25 to 1:3.3. Doping of CdS with Zn2+ and Cu2+ is found to enhance the PL intensity. PL band shows blue-shift and red-shift on doping with Zn2+ and Cu2+, respectively. UV and PL spectral features of the CdS/Au hybrid nanoparticles obtained by a physical mixing of CdS and Au nanoclusters in various volume ratios is also discussed. Au red-shifts and rapidly quenches the PL of CdS. An additional low energy band approximately 650 nm is observed in the UV visible spectrum of the hybrid nanoparticles.
Spectrochim Acta A Mol Biomol Spectrosc 2008 Dec 15
PMID:Studies on optical absorption and photoluminescence of thioglycerol-stabilized CdS quantum dots. 1854 55

Nanoparticles of Zn1-xCuxS with Cu concentrations of x=0.0, 0.1, 0.2, 0.3 and 0.4 were prepared by a co-precipitation reaction method from homogeneous solutions of zinc and copper salts. Both the ZnS and ZnS:Cu nanoparticles excited at about 370 nm exhibits a broad green emission band peaking around 491 nm, which confirms the characteristic feature of Zn2+ as well as Cu2+ ions as luminescent centers in the lattice. The TEM micrographs showed spherical morphology for ZnS nanocrystals and the average size of the particles was estimated to be around 8.5 nm. At liquid nitrogen temperature, ESR signal characteristic of Cu2+ ions was observed in samples of all concentrations. ESR spectra analysis also indicated that Cu2+ ions enter the host lattice by replacing Zn2+ ions with distorted tetrahedral site symmetry.
Spectrochim Acta A Mol Biomol Spectrosc 2008 Dec 15
PMID:ESR and photoluminescence properties of Cu doped ZnS nanoparticles. 1860 63

The pollen cone and the pollen grain of the two Argentinean species of Araucaria are described with LM, SEM and TEM. Primordia of pollen cones are formed in April and May and reach maturity by mid-October in A. angustifolia (Bert.) O. Kuntze and by mid-November in A. araucana. (Mol.) K. Koch. Characters of the mature pollen cones and microsporophylls between both taxa are clearly differentiated. Pollen grains are spheroidal-subspheroidal, inaperturate, and asaccate with granulate exine and a subequatorial annular area that corresponds to the sexine thickness. Sculpturing consists of irregularly dispersed granules that are sometimes fused to each other (A. angustifolia) or forming microrugulae (A. araucana). Microgranules and microspinules are also present. The pollen wall ultrastructure is formed by a granular ectexine and lamellated endexine. Granular elements in A. angustifolia are more loosely disposed, form more interstices, and are gradually smaller towards the endexine than in A. araucana. To asses the probable relationships within the family, we compared the pollen grains of the two Araucaria species with those of other extant genera (Agathis, Wollemia) and also with fossil pollen (Araucariacites, Balmeiopsis, Cyclusphaera, Dilwynites) attributed to Araucariaceae.
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PMID:Morphology and structure of the pollen cone and pollen grain of the Araucaria species from Argentina. 1866 23

The divergence of new gene functions is described by various scenarios that involve gene duplication, albeit, at fundamentally different stages. We performed experimental measurements and developed a subsequent model, aimed at predicting the rate of divergence under different scenarios. We used gene libraries of TEM-1 beta-lactamase that were drifted under purifying selection toward the original penicillinase activity or under no selection at all. The frequency of genes conferring a new function (degradation of a cephalosporin antibiotic) was measured at various stages of the drift, and a model that accounts for the differences in the observed adaptation dynamics of the drifting TEM-1 populations was derived. The results indicate that rapid nonfunctionalization in the population relieved from selection (Ohno's model) afforded only a narrow window of adaptation to cefotaxime (neofunctionalization). The trade-off between TEM-1's original function and the new evolving function also disfavored the "gene sharing" model. The rate of adaptation was maximal when selection for the original function was partially relieved to enable the accumulation of potentially adaptive mutations, while still purging a large fraction of otherwise deleterious mutations. Altogether, scenarios of subfunctionalization seem more feasible, whereby sustaining the original function by two copies facilitates the accumulation potentially adaptive mutations while purging nonfunctionalization mutations.
Mol Biol Evol 2008 Nov
PMID:Ohno's model revisited: measuring the frequency of potentially adaptive mutations under various mutational drifts. 1868 56


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