Spectroscopic

Two heterocyclic oximes (E)-N-hydroxy-1-(pyridin-2-yl)methanimine (Hp2ylm) and (E)-N-hydroxy-1-(pyridin-3-yl)methanimine (Hp3ylm) were synthesized from pyridine-2-carbaldehyde and pyridine-3-carbaldehyde, respectively.

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A new series of transition metal complexes of Co(III), Ni(II) and VO(IV) was synthesized with the bidentate Schiff base ligand (HL) derived from the condensation of 2-amino-3-benzyloxypyridine and 5-bromo salicylaldehyde.

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New ruthenium(III) complexes with 3-(Benzothiazol-2-yliminomethyl)-phenol (HL) ligand have been synthesized and characterized with the aid of elemental analysis, IR, electronic, and electron paramagnetic resonance spectroscopic techniques.

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A group of new fluoroaniline Schiff bases (3a–3f) were synthesized and structurally characterized by various spectroscopic techniques such as 1H-NMR, LC-MS and FT-IR spectral studies.

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The dinitrogenase component proteins of the conventional Mo nitrogenase (MoFe protein) and of the alternative Fe-only nitrogenase (FeFe protein) were both isolated and purified from Rhodobacter capsulatus, redox-titrated according to the same procedures and subjected to an EPR spectroscopic comparison. In the course of an oxidative titration of the MoFe protein (Rc1Mo) three significant S ¼ 1/2 EPR signals deriving from oxidized states of the P-cluster were detected: (1) a rhombic signal (g ¼ 2.07, 1.96 and 1.

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With the aim to distinguish between local and global conformational changes induced by trifluoroethanol in RNase A, spectroscopic and activity measurements in combination with proteolysis by unspecific proteases have been exploited for probing structural transitions of RNase A as a function of trifluoroethanol concentration. At 30% (v/v) trifluoroethanol (pH 8.0; 25 °C), circular dichroism and fluorescence spectroscopy indicate a cooperative collapse of the tertiary structure of RNase A coinciding with the loss of its enzymatic activity....

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A clear difference in the enthalpy changes derived from spectroscopic and calorimetric measurements has recently been shown. The exact interpretation of this deviation varied from study to study, but it was generally attributed to the non-two-state transition and heat capacity change. Although the temperature-dependent thermodynamics of the duplex formation was often implied, systemic and extensive studies have been lacking in universally assigning the appropriate thermodynamic parameter sets.

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Department of Chemistry ‘IFM’, University of Torino, Italy; 2Department of Biology, University ‘Roma Tre’, Rome, Italy; 3Department of Structural and Functional Biology, University of Insubria, Italy Haem binding to human serum albumin (HSA) endows the protein with peculiar spectroscopic properties. Here, the effect of ibuprofen and warfarin on the spectroscopic properties of ferric haem –human serum albumin (ferric HSA–haem) and of ferrous nitrosylated haem –human serum albumin (ferrous HSA –haem-NO) is reported.

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A comparative study of thermodynamic and kinetic aspects of Cu(II) and Ni(II) binding at the N-terminal binding site of human and bovine serum albumins (HSA and BSA, respectively) and short peptide analogues was performed using potentiometry and spectroscopic techniques. It was found that while qualitative aspects of interaction (spectra and structures of complexes, order of reactions) could be reproduced, the quantitative parameters (stability and rate constants) could not.

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Chlorite dismutase (EC 1.13.11.49), an enzyme capable of reducing chlorite to chloride while producing molecular oxygen, has been characterized using EPR and optical spectroscopy. The EPR spectrum of GR-1 chlorite dis-mutase shows two different high-spin ferric heme species, whichwe have designated
narrow(gx,y,z¼6.24, 5.42, 2.00) and
broad(gz,y,x ¼6.70, 5.02, 2.00).

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Thecaa3-oxidase from Thermus thermophilushas been studied with a combined electrochemical, UV/VIS and Fourier-transform infrared (FT-IR) spectroscopic approach. In this oxidase the electron donor, cytochromec, is covalently bound to subunit II of the cytochrome c oxidase. Oxidative electrochemical redox titrations in the visible spectral range yielded a midpoint potential of )0.01 ± 0.01 V (vs. Ag/AgCl/3MKCl, 0.218 V vs. SHE¢) for the hemec.

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The chemical structure of lipid A from the lipopolysaccha-ride of the mushroom-associated bacterium Pseudomonas reactans,a pathogen of cultivated mushroom, was elucida-ted by compositional analysis and spectroscopic methods (MALDI-TOF and two-dimensional NMR). The sugar backbone was composed of theb-(1¢fi6)-linkedD-gluco-samine disaccharide 1-phosphate.

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Small-angle neutron scattering experiments were performed on horse azidometmyoglobin (MbN3) at pressures up to 300 MPa.Other spectroscopic techniques have shown that a reorganization of the secondary structure and of the active site occur in this pressure range. The present measurements, performedusingvarious concentrations ofMbN3, showthat the compactness of the protein is not altered as the value of its radius of gyration remains constant up to 300 MPa.

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A new exocellular laccase was purified from the basidio-mycete C30. LAC2 is an acidic protein (pI¼3.2) prefer-entiallyproducedupona combined inductionby copper and p-hydroxybenzoate.The spectroscopic signature (UV/visible and EPR) of this isoform is typical of multicopper oxidases, but its enzymatic and physico-chemical properties proved to be markedly different from those of LAC1, the constitutive laccase previously purified from the same organism.

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Mature, active mammalian histidine decarboxylase is a di-meric enzyme of carboxy-truncatedmonomers (
53 kDa). By using a biocomputational approach, we have generateda three-dimensional model of a recombinant 1/512 fragment of the rat enzyme, which shows kinetic constants similar to those of the mature enzyme purified from rodent tissues. This model, together with previous spectroscopic data, al-lowed us to postulate that the occupation of the catalytic center by the natural substrate, or by substrate-analogs, would induce remarkable changes in the conformation of the intact holoenzyme....

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The cytochromec nitrite reductase is isolated from the membranes of the sulfate-reducing bacteriumDesulfovibrio desulfuricansATCC 27774 as a heterooligomeric complex composedby two subunits (61 kDa and19 kDa) containing c-type hemes, encoded by the genes nrfA and nrfH, respectively. The extracted complex has in average a 2NrfA:1NrfH composition. The separation of ccNiR sub-units from one another is accomplished by gel filtration chromatography in the presence of SDS.

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Plasmodium falciparumtriosephosphate isomerase (PfTIM) contains two tryptophan residues, W11 and W168. One is positioned in the interior of the protein, and the other is located on the active-site loop 6. Two single-tryptophan mutants, W11F and W168F, were constructed to evaluate the contributions of each chromophore to the fluorescence of the wild-type (wt) protein and to probe the utility of the residues as spectroscopic reporters.

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The major cellulase secreted by the filamentous fungus Trichoderma reeseiis cellobiohydrolase Cel7A. Its three-dimensional structure has been solved and various mutant enzymes produced. In order to study the potential use of T. reeseiCel7A in the alkaline pHrange, the thermal sta-bilityofCel7Awas studiedas a functionof pHwith thewild-type and two mutant enzymes using different spectroscopic methods. Tryptophan fluorescence and CD measurements of the wild-type enzyme show an optimal thermostability between pH3.5–5.

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Specific lipids of the purple membrane ofHalobacteriaare required for normal bacteriorhodopsin structure, function, and photocycle kinetics [Hendler, R.W. & Dracheva, S. (2001) Biochemistry (Moscow)66, 1623–1627]. The decay of the M-fast intermediate through a path including the O intermediate requires the presence of a hydrophobic envi-ronment near four charged aspartic acid residues within the cytoplasmic loop region of the protein (R. W. Hendler & S. Bose, unpublished results).

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Studies on horseradish peroxidase C and other haem peroxidases have been carried out on selected mutants in the distal haem cavity providing insight into the functional importance of the distal residues. Recent work has dem-onstrated that proximal structural features can also exert an important influence in determining the electronic structure of the haem pocket.

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