Effect of beta-lactamase-catalyzed hydrolysis of cephalosporins on peroxynitrite-mediated nitration of serum albumin and cytochrome c

The hydrolysis of beta-lactam antibiotics by beta-lactamases is one of the major bacterial defense systems. These enzymes generally hydrolyze a variety of antibiotics including the latest generation of cephalosporins, cephamycins and imipenem. In this paper, the effect of cephalosporins-based antibiotics on the peroxynitrite-mediated nitration of protein tyrosine is described. Although some of the antibiotics have weak inhibitory effect on the nitration reactions in the absence of beta-lactamase, they exhibit very strong inhibition in the presence of beta-lactamase. This is due to the elimination of heterocyclic thiol/thione moieties from cephalosporins by beta-lactamase-mediated hydrolysis. After the elimination, the thiols/thiones effectively scavenge peroxynitrite, leading to the inhibition of the nitration reactions.

Observation of Water-Mediated Helix-Terminating Conformation in a Dehydrophenylalanine Peptide: Crystal and Solution Structure of the Octapeptide Ac-.DELTA.Phe-Val-.DELTA.Phe-Phe-Ala-Val-.DELTA.Phe-Gly-OMe

We have synthesised and determined the solution conformation and X-ray crystal structure of the octapeptide Ac-Delta Phe(1)-Val(2)-Delta Phe(3)-Phe(4)-Ala(5)-Val(6)-Delta Phe(7)-Gly(8)-OCH3 (Delta Phe = alpha,beta-dehydrophenylalanine) containing three Delta Phe residues as conformation constraining residues. In the solid state, the peptide folds into (i) an N-terminal (3)10(R)-helical pentapeptide segment, (ii) a middle non-helical segment, and (iii) a C-terminal incipient (3)10(L)-helical segment. The results of H-1 NMR data also suggest that a similar multiple-turn conformation for the peptide is largely maintained in solution. Though the C-terminal helix is incipient, the overall conformation of the octapeptide matches well with the conformation of the hairpins reported. Comparison of the pi-turn seen in the octapeptide molecule with those observed in proteins at the C-terminal end of helixes shows the structural similarity among them. A water molecule mediates the 5 --> 2 hydrogen bond in the pi-turn region. This is the first example of a water-inserted pi-turn in oligopeptides reported so far. Comparison between the present octapeptide and another (3)10(R)-helical dehydro nonapeptide Boc-Val-Delta Phe-Phe-Ala-Phe-Delta Phe-Val-Delta Phe-Gly-OCH3 solved by us recently, demonstrates the possible sequence-dependent conformational variations in alpha,beta-dehydrophenylalanine-containing oligopeptides.

Organic Additive-Mediated Synthesis of Novel Cobalt(II) Hydroxides

Electrochemical precipitation of cobalt(II) hydroxide from nitrate solutions containing organic molecules, such as glucose, fructose, lactose, glycerol, and citric acid, yields a new modification of cobalt (II) hydroxide (a = 3.09 +/- 0.03 Angstrom, c = 23.34 +/- 0.36 Angstrom) that is isostructural with cu-nickel hydroxide; precipitation in the absence of organic additives gives the stable, brucite-like, beta-CO (OH)(2). (C) 1995 Academic Press, Inc.

Reductive dimerization of organic thiocyanates to disulfides mediated by tetrathiomolybdate

An interesting reductive dimerization of organic thiocyanates assisted by benzyltriethylammonium tetrathiomolybdate, [(PhCH(2)NEt(3))(2)MoS4], 1, leads to the formation of the corresponding disulfides in high yields.

Surface resistance and residual losses of Ag?doped YBa2Cu3O7?? thin films on sapphire

High?quality Ag?doped YBa2Cu3O7?? thin films have been grown by laser ablation on R?plane ?1102? sapphire without any buffer layer. Thin films have been found to be highly c?axis oriented with Tc=90 K, transition width ?T?1 K, and transport Jc=1.2×106 A?cm?2 at 77 K in self?field conditions. The microwave surface resistance of these films measured on patterned microstrip resonators has been found to be 530 ?? at 10 GHz at 77 K which is the lowest reported on unbuffered sapphire. Improved in?plane epitaxy and reduced reaction rate between the substrate and the film caused due to Ag in the film are believed to be responsible for this greatly improved microwave surface resistance. © 1995 American Institute of Physics.

Multifunctional cryogenic sensors from n-BaTiO3 ceramics having strong negative temperature coefficient of resistance

Donor-doped n-BaTiO3 polycrystalline ceramics show a strong negative temperature coefficient of resistivity below the orthorhombic-rhombohedral phase transition point, from 10(2-3) Omega cm af 190 K to 10(10-13) Omega cm at less than or similar to 50 K, with thermal coefficient of resistance alpha = 20-23% K-1. Stable thermal sensors for low-temperature applications are realized therefrom. The negative temperature coefficient of resistivity region can be modified by substituting isovalent ions in the lattice. Highly nonlinear current-voltage (I-V) curves are observed at low temperatures, with a voltage maximum followed by the negative differential resistance. The I-V curves are sensitive to dissipation so that cryogenic sensors can be fabricated for liquid level control, flow rate monitoring, radiation detection or in-rush voltage limitation.

7Li and 23Na NMR studies of transmembrane cation transport mediated by ionophore lasalocid A

Ion transport across phospholipid vesicles was studied by 7Li and 23Na-NMR using an aqueous anionic paramagnetic shift reagent, dysprosium nitrilotriacetate [Dy(NTA)2]3?, mediated by ionophores, lasalocid A and A23187. The intra- and extracellular 7Li and 23Na-NMR signals were well separated (20?Hz) at mM concentration of the shift reagent. The observed data on the rate constant for lithium transport across DPPC vesicles at various concentrations of the ionophores indicated that lasalocid A is a more efficient carrier for lithium ion compared with the sodium ion transport by this ionophore, while A23187 was not specific to either of the ions (Li or Na). ©1998 European Peptide Society and John Wiley & Sons, Ltd.

Estimating the Threshold Surface Density of Gp120-CCR5 Complexes Necessary for HIV-1 Envelope-Mediated Cell-Cell Fusion

Reduced expression of CCR5 on target CD4(+) cells lowers their susceptibility to infection by R5-tropic HIV-1, potentially preventing transmission of infection and delaying disease progression. Binding of the HIV-1 envelope (Env) protein gp120 with CCR5 is essential for the entry of R5 viruses into target cells. The threshold surface density of gp120-CCR5 complexes that enables HIV-1 entry remains poorly estimated. We constructed a mathematical model that mimics Env-mediated cell-cell fusion assays, where target CD4(+)CCR5(+) cells are exposed to effector cells expressing Env in the presence of a coreceptor antagonist and the fraction of target cells fused with effector cells is measured. Our model employs a reaction network-based approach to describe protein interactions that precede viral entry coupled with the ternary complex model to quantify the allosteric interactions of the coreceptor antagonist and predicts the fraction of target cells fused. By fitting model predictions to published data of cell-cell fusion in the presence of the CCR5 antagonist vicriviroc, we estimated the threshold surface density of gp120-CCR5 complexes for cell-cell fusion as similar to 20 mu m(-2). Model predictions with this threshold captured data from independent cell-cell fusion assays in the presence of vicriviroc and rapamycin, a drug that modulates CCR5 expression, as well as assays in the presence of maraviroc, another CCR5 antagonist, using sixteen different Env clones derived from transmitted or early founder viruses. Our estimate of the threshold surface density of gp120-CCR5 complexes necessary for HIV-1 entry thus appears robust and may have implications for optimizing treatment with coreceptor antagonists, understanding the non-pathogenic infection of non-human primates, and designing vaccines that suppress the availability of target CD4(+)CCR5(+) cells.

The two-step positive temperature coefficient in resistance characteristics of n-(Ba,Pb)TiO3 ceramics created through inclusion of grain boundary modifier additives

Donor-doped n-(Ba,Pb)TiO3 polycrystalline ceramics exhibit distinctly two-step positive temperature coefficient of resistance (PTCR) characteristics when formulated with suitable combinations of B2O3 and Al2O3 as grain boundary modifiers by heterogeneous addition. B2O3 or Al2O3 when added singularly resulted in either steep or broad PTCR jumps respectively across the phase transition. The two-step PTCR is attributed to the activation of the acceptor states, created through B2O3 and Al2O3, for various temperature regimes above the Curie point (T-c). The changing pattern of trap states is evident from the presence of Ti4+-O--Al3+ type hole centres in the grain boundary layer regions, identified in the electron paramagnetic resonance (EPR) spectra. That charge redistribution occurs among the inter-band gap defect states on crossing the Curie temperature is substantiated by the temperature coefficient in the EPR results. Capacitance-voltage results clearly show that there is an increase in the density of trap states with the addition of B2O3 and Al2O3. The spread in energy values of these trap states is evident from the large change in barrier height (phi similar or equal to 0.25-0.6 eV) between 500 and 650 K.

Water-mediated ionic interactions in protein structures

It is well known that water molecules play an indispensable role in the structure and function of biological macromolecules. The water-mediated ionic interactions between the charged residues provide stability and plasticity and in turn address the function of the protein structures. Thus, this study specifically addresses the number of possible water-mediated ionic interactions, their occurrence, distribution and nature found in 90% non-redundant protein chains. Further, it provides a statistical report of different charged residue pairs that are mediated by surface or buried water molecules to form the interactions. Also, it discusses its contributions in stabilizing various secondary structural elements of the protein. Thus, the present study shows the ubiquitous nature of the interactions that imparts plasticity and flexibility to a protein molecule.

One pot conversion of alcohols to disulfides mediated by benzyltriethylammonium tetrathiomolybdate

A one pot conversion of alcohols to disulfides in good yields via the activation of a hydroxyl group with DCC or P(NMe2)(3) / CCl4 followed by treatment with benzyltriethylammonium tetrathiomolybdate is reported. (C) 1999 Elsevier Science Ltd. All rights reserved.

Preincubation of cut tobacco leaf explants promotes Agrobacterium-mediated transformation by increasing vir gene induction

The effects of preincubation of cut tobacco leaf explants on Agrobacterium transformation efficiency and induction of Agrobacterium virE-lacZ fusion were evaluated. Transformation efficiency was evaluated by histochemical and fluorometric analysis of beta-glucuronidase in leaf rings transformed with Agrobacterium tumefaciens strain LBA4404(pKIWI105). The transformation efficiency increased by 2-fold, 5-fold, and 4.3-fold upon preincubation for 24, 48, and 72 h, respectively. Preincubation for 24, 48, and 72 h increased the ability of tobacco leaf segments to induce Agrobacterium virE by 2.3-fold, 3.5-fold and 4.5-fold, respectively. The requirement of preincubation for increased transformation efficiency was obviated by the addition of 100 mu M acetosyringone to the freshly cut leaf rings cocultivated with Agrobacterium. The production of vii gene inducers by the leaf rings during the preincubation period is an important factor that contributes to increased transformation efficiency of Agrobacterium upon preincubation. (C) 1999 Elsevier Science Ireland Ltd. All rights reserved.

Regioselective synthesis of bicyclo[4.2.1]nonane-2,8-diones via BF3.Et2O mediated intramolecular diazo ketone insertion reaction

Treatment of the diazo diones 11a-d with boron trifluoride diethyl etherate furnished the bicyclo[4.2.1]nonane-2,g-diones 15a-d in a highly regioselective manner. (C) 1999 Elsevier Science Ltd. All rights reserved.

Tracking and erosion resistance of silicone rubber nanocomposites under positive and negative dc voltages

ASTM D2303 standard provides a method for evaluating the tracking and erosion resistance of polymeric insulators under ac voltages. In this paper, the above method has been extended for evaluating the performance of the insulators under dc stresses. Tests were conducted on polymeric silicone rubber (SR) insulators under positive and negative dc stresses. Micron sized Alumina trihydrate (uATH) and nano sized Alumina (nALU) were used as fillers in SR matrix to improve the resistance to tracking and erosion. Results suggest that SR composites perform better under negative dc than under positive dc voltages. Eroded mass and leakage current data support the above result. Samples with low concentration of nano alumina fillers performed on par with the samples with large loadings of uATH.