EPR properties of mixed-valent μ-oxo and μ-hydroxo dinuclear iron complexes produced by radiolytic reduction at 77 K

 Radiolytic reduction at 77 K of oxo-/hydroxo-bridged dinuclear iron(III) complexes in frozen solutions forms kinetically stabilized, mixed-valent species in high yields that model the mixed-valent sites of non-heme, diiron proteins. The mixed-valent species trapped at 77 K retain ligation geometry similar to the initial diferric clusters. The shapes of the mixed-valent EPR signals depend strongly on the bridging ligands. Spectra of the Fe(II)OFe(III) species reveal an S=1/2 ground state with small g-anisotropy as characterized by the uniaxial component (g _z –g _av /2<0.03) observable at temperatures as high as ∼100 K. In contrast, hydroxo-bridged mixed-valent species are characterized by large g-anisotropy (g _z –g _av /2>0.03) and are observable only below 30 K. Annealing at higher temperatures causes structural relaxation and changes in the EPR characteristics. EPR spectral properties allow the oxo- and hydroxo-bridged, mixed-valent diiron centers to be distinguished from each other and can help characterize the structure of mixed-valent centers in proteins. Received: 27 June 1998 / Accepted: 25 February 1999     

The lifetime of molecular (Davydov) solitons

The lifetime of Davydov solitons in a one-dimensional system is studied theoretically. The process of thermalization and the properties of solitons at finite temperature are investigated and the processes of soliton creation and disintegration are discussed.     

Changes in synapses after gamma-irradiation of the rat head

High reactivity and, at the same time, flexibility of interneuronal contacts were observed after exposure of rat head to 2-100 Gy radiation. At high doses (200-400 Gy) radiation-induced changes played a major role in the development of the cerebral form of radiation sickness. A complete asynapsis is probably one of the causes of the animals death "under the ray" (irradiation of the head with a dose of 1000 Gy).     

Water Balance in Cucumis Plants, Measured by Nuclear Magnetic Resonance, I

In this paper we demonstrate the study of plant water balanceby the non-invasive measurement of tissue water content andwater flow using proton nuclear magnetic resonance (NMR). Sapvelocity and flux were measured independently in the presenceof an excess of stationary tissue water. The instrumentationdescribed allows automated and unattended measurement of flow-and water content-variables in a well-defined region of theplant over periods of several days, with a time resolution betweensuccessive measurements of c. 5 s. Using this apparatus theeffect of changes in light intensity (day/night rhythm) andrelative humidity on stem tissue water content as well as onthe velocity and flux of xylem sap in the stem were investigatedin a cucumber plant. The results are in agreement with predictionsfrom a simple model for plant water balance, which is basedon water potential, flow rate and resistance to flow. As longas only transpiration is varied, flow rate and water content(or potential) are affected in opposite ways as demonstratedin this paper. In contrast, the model predicts that changesin uptake (resulting from changes in, for example, root resistance)will induce changes in water content and flow in the same direction.An experimental verification of this prediction is given ina subsequent paper, where, in addition, the NMR results arecompared to those obtained with a dendrometer. Key words: Water balance model, Cucumis sativus L., flow, water content, NMR, water balance measurement     

TASTE GROUP THRESHOLDS AND SENSORY EVALUATION OF SPANISH WINE VINEGARS

Wine vinegar is a product obtained from wine acidification which contains at least 5% by wt. of acetic acid, in general without any additives or colorings.
Aspects studied in this work include: the determination of the taste group thresholds (geometric mean of the individual best-estimate thresholds "BET") of two different acids (citric and acetic acids) in aqueous solution and spanish vinegars produced from table and sherry wines. The results obtained suggest that wine vinegar can be considered something more than just an acidulant agent.
In order to evaluate differences among wine vinegars, discriminant tests for twenty-five spanish vinegars (sherry, table and flavored vinegars) were applied. Six of the twelve attributes freely chosen by assessors allowed grouping of the spanish wine vinegars according to their sensory aspects.     

Arginine deprivation in KB cells: I. Effect on cell cycle progress

When exponentially growing KB cells were deprived of arginine, cell multiplication ceased after 12 h but viability was maintained throughout the experimental period (42-48 h). Although tritiated thymidine ([(3)H]TdR) incorporation into acid-insoluble material declined to 5 percent of the initial rate, the fraction of cells engaged in DNA synthesis, determined by autoradiography, remained constant throughout the starvation period and approximately equal to the synthesizing fraction in exponentially growing controls (40 percent). Continous [(3)H]TdR-labeling indicated that 80 percent of the arginine-starved cells incorporated (3)H at some time during a 48-h deprivation period. Thus, some cells ceased DNA synthesis, whereas some initially nonsynthesizing cells initiated DNA synthesis during starvation. Flow microfluorometric profiles of distribution of cellular DNA contents at the end of the starvation period indicated that essentially no cells had a 4c or G2 complement. If arginine was restored after 30 h of starvation, cultures resumed active, largely asynchronous division after a 16-h lag. Autoradiographs of metaphase figures from cultures continuously labeled with [(3)H]TdR after restoration indicated that all cells in the culture underwent DNA synthesis before dividing. It was concluded that the majority of cells in arginine-starved cultures are arrested in neither a normal G1 nor G2. It is proposed that for an exponential culture, i.e. from most positions in the cell cycle, inhibition of cell growth after arginine with withdrawal centers on the ability of cells to complete replication of their DNA.     

A Large-Scale Allosteric Transition in Cytochrome P450 3A4 Revealed by Luminescence Resonance Energy Transfer (LRET)

Effector-induced allosteric transitions in cytochrome P450 3A4 (CYP3A4) were investigated by luminescence resonance energy transfer (LRET) between two SH-reactive probes attached to various pairs of distantly located cysteine residues, namely the double-cysteine mutants CYP3A4(C64/C468), CYP3A4(C377/C468) and CYP3A4(C64/C121). Successive equimolar labeling of these proteins with the phosphorescent probe erythrosine iodoacetamide (donor) and the near-infrared fluorophore DY-731 maleimide (acceptor) allowed us to establish donor/acceptor pairs sensitive to conformational motions. The interactions of all three double-labeled mutants with the allosteric activators α-naphthoflavone and testosterone resulted in an increase in the distance between the probes. A similar effect was elicited by cholesterol. These changes in distance vary from 1.3 to 8.5 Å, depending on the position of the donor/acceptor pair and the nature of the effector. In contrast, the changes in the interprobe distance caused by such substrates as bromocriptine or 1-pyrenebutanol were only marginal. Our results provide a decisive support to the paradigm of allosteric modulation of CYP3A4 and indicate that the conformational transition caused by allosteric effectors increases the spatial separation between the beta-domain of the enzyme (bearing residues Cys₆₄ and Cys₃₇₇) and the alpha-domain, where Cys₁₂₁ and Cys₄₆₈ are located.     

Synthesis of Nitrogen Oxides in a Subthreshold Microwave Discharge in Air and in Air Mixtures with Methane

Plasma Physics Reports - A subthreshold discharge excited by a microwave beam in air at pressures close to atmospheric is studied as a plasmachemical method of nitrogen oxide (NOx) production. It...     

The Change in the Linear Energy Transfer of a Clinical Proton Beam in the Presence of Gold Nanoparticles

Biophysics - Gold nanoparticles are promising radiosensitizers for proton radiotherapy. However, the physical mechanisms of gold nanoparticles radiosensitization remain unclear. In the present...     

Production of endothelial progenitor cells obtained from human Wharton's jelly using different culture conditions

Endothelial progenitor cells (EPC) participate in revascularization and angiogenesis. EPC can be cultured in vitro from mononuclear cells of peripheral blood, umbilical cord blood or bone marrow; they also can be transdifferentiated from mesenchymal stem cells (MSC). We isolated EPCs from Wharton's jelly (WJ) using two methods. The first method was by obtaining MSC from WJ and characterizing them by flow cytometry and their adipogenic and osteogenic differentiation, then applying endothelial growth differentiating media. The second method was by direct culture of cells derived from WJ into endothelial differentiating media. EPCs were characterized by morphology, Dil-LDL uptake/UEA-1 immunostaining and testing the expression of endothelial markers by flow cytometry and RT-PCR. We found that MSC derived from WJ differentiated into endothelial-like cells using simple culture conditions with endothelium induction agents in the medium.