Polyethylene glycol in aqueous solution: solvent perturbation and gel filtration studies

The in vitro blastogenic response of spleen cells to phytohemagglutinin-M (PHA) was evaluated as a measurement of the immunologic reactivity of virgin, pregnant and post-partum mice. In PHA-stimulated cultures 3H-thymidine incorporation by lymphocytes from post-partum mice was not significantly different from that of virgin age-matched control mice. Background 3H-thymidine incorporation was high in cultures from post-partum mice resulting in stimulation indices which were lower than those of virgin controls. Spleen cells from mice sacrificed after various intervals of pregnancy showed depressed PHA responsiveness only at the 15th day of gestation. The PHA response of normal spleen cells was depressed in the presence of serum from pregnant or post-partum mice.     

Antioxidant activity of reduced menadione in solvent solution and in model membranes

The antioxidant activity of reduced menadione was investigated and compared with that of alpha-tocopherol both in solvent solution and in large unilamellar vesicles by using azocompounds as free radical generators. The results show that: i) reduced menadione behaves as a chain-breaking antioxidant; ii) its inhibition rate constant is similar to that of alpha-tocopherol in homogeneous solution, whereas it is 4 times larger in egg yolk lecithin vesicles; iii) the stoichiometric factor is found lower than 1 in both systems, since a substantial portion of menadiol is consumed by autoxidation and does not contribute to radical trapping; iv) when both alpha-tocopherol and menadiol are present in vesicles, reduced menadione can spare alpha-tocopherol. Data presented here suggest that the reduced form of vitamin K may protect, when present, cellular membranes from free radical damage.     

Luminescence and structure of the protonated forms of meso-tetraarylporphyrins in solution

A distillate of light alkylate naphtha (CAS number 64741-66-8; LAN distillate) was administered via inhalation, 6 h/d, 7 d/wk to 4 groups of Sprague-Dawley rats (10/sex/dose) at target concentrations of 0 (filtered air control), 5, 12.5, or 25 g/m3 with the highest dose exceeding 60% of the lower explosive limit of LAND. Exposure began 2 wk prior to mating and continued throughout gestation until postnatal d 4 for females or for 8 consecutive weeks for males. No apparent clinical signs indicative of systemic toxicity were observed in the F0 and F1 animals of either sex. Inhalation exposure to LAND up to and including the 25 g/m3 dose level had no effect on parental food consumption, body weights, absolute and relative organ weights, and reproductive indices. All groups had comparable delivery data and a fertility index > or 80%. Pups in all groups showed comparable birth weights, weight gain, a viability index (postnatal d 4) for all groups of > or = 97%, and no histopathological changes. In the dams, there were no significant differences in the mean numbers of corpora lutea, implantation sites, and resorptions recorded at necropsy. In the males, the only remarkable findings at necropsy were a small right epididymis and testis seen in one mid-dose male and an abscess on the right epididymis of a high-dose male. In both cases, the dams that had been bred to these males produced normal litters. There were no test material-related microscopic changes observed in the testes and epididymis of the F0 male rats or ovaries of the F0 female rats exposed to LAND. Under the conditions of this experiment, the no-observed-adverse-effect level (NOAEL) for LAND via inhalation in rats is established at greater than 24.7 g/m3 (analytical concentration).     

Investigation of secondary and tertiary structural changes of cytochrome c in complexes with anionic lipids using amide hydrogen exchange measurements: an FTIR study

The structure of cytochrome c bound to anionic lipid membranes composed of dimyristoyl, dipalmitoyl, or dioleoyl phosphatidylglycerols, or of bovine heart cardiolipin, has been investigated by Fourier transform infrared spectroscopy. Only small changes in secondary structure, as registered by the amide I band of cytochrome c, were observed upon binding at temperatures below that of denaturation of the protein, and these were not coupled to the thermotropic phase transitions of the lipid. The denaturation temperature of the protein decreased by approximately 25-30 degrees upon binding, in a progression which correlated with that of the lipid phase transition temperatures, being approximately 7 degrees lower for complexes with dioleoyl than with dipalmitoyl phosphatidylglycerol. Large changes in the amide proton exchange characteristics, as monitored by the spectral shifts in the amide I band of the protein in D2O, were observed on binding cytochrome c to the lipid membranes. For the slowly exchanging population, the amide deuteration rates of the free protein were nearly independent of temperature, whereas those of the bound protein increased by up to two orders of magnitude over the temperature range from 10 to 40 degrees C. In addition, the extent of exchange differed between the bound and unbound protein. A structural transition in the bound protein was detected as a discontinuous step in Arrhenius plots of the deuterium exchange rates which occurred at a temperature in the region of 22 to 29 degrees C, depending on the lipid, far below that of denaturation. The temperature of this transition was determined by the physical state of the lipid, being 7 degrees lower for the lipids in the fluid state than for those in the gel state, and, for complexes with dimyristoyl phosphatidylglycerol, occurred at an intermediate temperature, being controlled by the lipid chain-melting transition at 27-28 degrees C. These results provide evidence for a coupling of the tertiary structure of the membrane-bound protein with the physical state of the membrane lipids.     

Cloning and biochemical characterization of an anionic peroxidase from Zea mays

We have isolated, cloned and characterized a cDNA from Zea mays L., denoted ZmAP1, coding for an anionic peroxidase. The open reading frame of ZmAP1 starting 72 residues from the 5' end of the cDNA predicts a 37,778 dalton protein of 356 amino acid residues. The protein has high similarity to other peroxidases and contains two peroxidase motifs that carry two highly conserved histidines in the active center. We expressed recombinant ZmAP1 protein in E. coli as a fusion with maltose-binding protein. The fusion protein was biochemically active after addition of hemin to the apoprotein. The maize peroxidase ZmAP1 has a pH optimum at pH 4.0 and a Km of 0.2 mM for the substrate 2,2'-azino-bis-(3-ethyl-benzothiazolin-6-sulfonic acid) at this pH. In maize seedlings the ZmAP1 gene is expressed predominantly in roots, the mesocotyl, the coleoptile and to a lower extent in the node, whereas no expression in the primary leaf was found. In situ hybridization shows that the expression of ZmAP1 in the young maize root is confined to the epidermis, hypodermis and the pericycle.     

Purification and characterization of two forms of urokinase

Affinity chromatography on agmatine-Sepharose was used for the separation of two active forms of urokinase (EC 3.4.99.26) from partially purified human urinary urokinase. The approximate molecular weight of the heavier form was 47 000 and of the lighter 33 400. Both forms were homogeneous by sodium dodecyl sulfate gel electrophoresis and by 3H-labeled diisopropylphosphorofluoridate and 14C-labeled p-nitrophenyl-p'-guanidinobenzoate incorporation studies. The 33 400 mol. wt. form had a single chain, and the 47 000 mol. wt. form had two chains (33 100 and 18 600 mol. wt.) linked by disulfide bonds. The specific activity of the heavier form was 104 000 CTA units/mg protein, compared with 226 000 units/mg for the lighter form but the activities per mmol of active site (molar activities) of the two forms were almost identical (9.6-10(9) and 10.2-10(9) CTA units/mmol). Isoelectric focusing on gels showed that the 47 000 material contained one major subform with a pI of 8.60 and a minor subform with a pI of 8.90, while the 33 400 material had three major subforms with pI values of 8.35, 8.60 and 8.70, respectively, and a minor subform with a pI of 8.05. 3H-labeled diisopropylphosphorofluoridate incorporation studies revealed an active-site serine residue in the heavy chain.     

Three-dimensional solution structure of alpha-conotoxin MII by NMR spectroscopy: effects of solution environment on helicity

alpha-Conotoxin MII, a 16-residue polypeptide from the venom of the piscivorous cone snail Conus magus, is a potent and highly specific blocker of mammalian neuronal nicotinic acetylcholine receptors composed of alpha3 beta2 subunits. The role of this receptor type in the modulation of neurotransmitter release and its relevance to the problems of addiction and psychosis emphasize the importance of a structural understanding of the mode of interaction of MII with the alpha3 beta2 interface. Here we describe the three-dimensional solution structure of MII determined using 2D 1H NMR spectroscopy. Structural restraints consisting of 376 interproton distances inferred from NOEs and 12 dihedral restraints derived from spin-spin coupling constants were used as input for simulated annealing calculations and energy minimization in the program X-PLOR. The final set of 20 structures is exceptionally well-defined with mean pairwise rms differences over the whole molecule of 0.07 A for the backbone atoms and 0.34 A for all heavy atoms. MII adopts a compact structure incorporating a central segment of alpha-helix and beta-turns at the N- and C-termini. The molecule is stabilized by two disulfide bonds, which provide cross-links between the N-terminus and both the middle and C-terminus of the structure. The susceptibility of the structure to conformational change was examined using several different solvent conditions. While the global fold of MII remains the same, the structure is stabilized in a more hydrophobic environment provided by the addition of acetonitrile or trifluoroethanol to the aqueous solution. The distribution of amino acid side chains in MII creates distinct hydrophobic and polar patches on its surface that may be important for the specific interaction with the alpha3beta2 neuronal nAChR. A comparison of the structure of MII with other neuronal-specific alpha-conotoxins provides insights into their mode of interaction with these receptors.     

Enhanced carbon solubility in solvent for SiC rapid solution growth:Thermodynamic evaluation of Cr-Ce-Si-C system

The carbon dissolution in solvent plays a key role in the process of solution growth route for SiC single crystal,which could determine the growth rate and quality of the products.However,the carbon dissolving ability of binary alloy solvent still needs to be improved.Here,we demonstrate the improved carbon dissolution and enlarged carbon supersaturation in Cr-Ce-Si ternary solvent,showing great potential for SiC solution growth.The phase relations of Cr-Ce-Si-C system were determined by using C...     

A study of solvent effects on the phosphorescence properties of flavins

A combination of zero field triplet state techniques are used to study the excited electronic states of a series of flavin and flavin related molecules both in single crystals and glass matrices. Particular attention is given to the effects of solvent interaction on the triplet state properties of the flavin molecules. The total phosphorescence decay rate constants at 1.4 degrees K are reported for the flavin molecules in polar and nonpolar solvents. The rate constants are then correlated to the degree of solvent interaction. Results indicate possible complex formation between the isoalloxazine and adenine groups in FAD. Finally, the results and possible interpretation on the study of a flavoenzyme, L-amino acid oxidase are presented.     

Synthesis and characterization of mesostructured ceria-zirconia solid solution

Mesostructured Ce0.6Zr0.4O2 solid solutions were synthesized by coprecipitation combined with evaporation-induced self-assembly process. The obtained materials were characterized by X-ray diffractometer (XRD), Raman, transmission electron microscopy (TEM), N2 sorption, and hydrogen temperature programmed reduction (H2-TPR). The results showed that the solid solutions consisted of uniform nanocrystals, which piled homogeneous mesopores of about 4 nm. Furthermore, different surfactants had little influence on the mesoporous structures. All these samples exhibited high thermal stability.     

Separation of platinum and palladium from chloride solution by solvent extraction using Alamine 300

The separation of platinum and palladium from chloride solution by solvent extraction, using Alamine 300 as an extractant, has been studied. The effect of different parameters such as the concentration of HCl in the feed solution, NaCl concentration, extractant concentration, and platinum and palladium concentrations in the feed solution has been evaluated. Stripping behavior was also studied using different stripping agents, such as sodium thiocyanate and thiourea. Using a saturated solution of sodium chloride at a pH 1.5, platinum was selectively extracted as the major component, along with minor amounts of palladium. By adding a saturated solution of NaCl to the aqueous phase, palladium extraction could be decreased. Additionally, with the use of 0.5 M HCl in place of NaCl, both metals were studied. Selective stripping of platinum accomplished using sodium thiocyanate, and the selective removal palladium was achieved with sodium thiosulfate. This process can achieve a 99.9% purity of platinum even in very dilute solution.     

Perplexing effects of hippocampal lesions on latent inhibition: a neural network solution

Experimental data indicate that hippocampal lesions might impair, spare, or even facilitate latent inhibition (LI). Furthermore, when LI is impaired by the lesions, it might be reinstated by haloperidol administration. The present article applies a neural network model of classical conditioning (N. A. Schmajuk, Y. W. Lam, & J. A. Gray, 1996) to investigate the possible causes of these puzzling results. According to the model, LI is manifested because preexposure of the conditioned stimulus (CS) reduces Novelty, defined as proportional to the sum of the mismatches between predicted and observed events, thereby reducing attention to the CS and retarding conditioning. It is assumed that hippocampal lesions affect the prediction of events. Computer simulations reveal that, depending on the behavioral protocol (i.e., procedure and total time of CS preexposure), Novelty in hippocampal lesioned animals might be larger, equal, or smaller (corresponding to smaller, equal, or larger LI) than in normal controls. Reinstatement of LI by haloperidol administration is explained by assuming that dopaminergic antagonists decrease the value of Novelty, when Novelty increases following hippocampal lesions.     

微量杂质在工业纯钛中的存在形式及其对力学性能的影响

采用差示扫描量热法(DSC)、X射线衍射(XRD)、扫描电镜及其附带的能谱仪(SEM+EDS)、电子探针(EPMA)等分析方法和力学性能测试,研究常温下铁、硅、氯、氮、氧、碳(Fe,Si,Cl,M,O,C)等杂质在工业纯钛中的存在形式、分布状况及其对力学性能的影响。结果表明:在工业纯钛中,铁、硅、氯杂质元素的微区元素浓度较低,只有极少区域存在偏聚;碳元素分布不均匀,微区偏聚现象明显;氧元素在工业纯钛中含量较少且分布均匀;随铁、氮、氧、碳、氯等杂质含量增加,工业纯钛的强度和硬度大幅提高,塑韧性显著降低,最大硬度HB增幅为24,屈服强度和抗拉强度的最大增加幅度分别为144 MPa和122 MPa,伸长率的减幅最大为19.8%。     

Purification and characterization of maize starch synthase I and its truncated forms

A number of imidazole-based compounds were tested for their utility as (1)H NMR molecular probes of intracellular pH. Imidazole, previously found useful as a probe of erythrocyte pH, reported a pH in perfused canine glioma cells that was more than 1 pH unit lower than that reported by inorganic phosphate, consistent with the known lysosomal compartmentation of the molecule. Imidazole acetate, also proposed as an NMR probe of cellular pH, was found not to enter the cells of this study. Histidine was found to be readily taken up by cells and reported a pH consistent with that reported by inorganic phosphate. Using the chemical shift of the histidine H2 proton in cells incubated with 10 mM histidine, cellular pH measurements could be obtained in less than 1 s. This compares quite favorably with the measurement time, typically several minutes, needed to assess in vivo pH by (31)P NMR. The use of histidine as a probe of pH is demonstrated in perfused canine and rat glioma cells subjected to ischemia or to low extracellular pH.     

The matrix effects on kinetic rate constants of antibody-antigen interactions reflect solvent viscosity

This study describes the influence of different matrices on two model antibody-antigen interactions; that between beta2microglobulin and anti beta2microglobulin, and that of rabbit anti mouse Fc fragment (RAMFc) with mouse IgG. The matrices investigated were; phosphate-buffered saline pH 7.4 containing 0.05% Tween 20 detergent, horse serum, a 50:50 mixture of phosphate-buffered saline/Tween 20 and horse serum, and four glycerol solutions of differing concentrations. A recently developed optical biosensor, the IAsys, was used to monitor the interactions in real-time and provide precise determinations of k(ass), k(diss) and KA values. The results show that the rates of association and dissociation for the two different antibody:antigen models are significantly affected by the surrounding matrix. Glycerol of known viscosity was used as a matrix in both models to show that this effect is attributable to the viscosity as opposed to proteins present in the matrix. The viscosity of the matrix has also been shown to have an apparent influence upon the overall equilibrium/affinity constant for the interaction, with measurements of KA tending to increase with viscosity. The significant effects of matrix on kinetic rate constants for antibody-antigen interactions shown here have important implications in the use of immunoassays where non-equilibrium measurements are made in serum matrices.     

Native-like beta-hairpin structure in an isolated fragment from ferredoxin: NMR and CD studies of solvent effects on the N-terminal 20 residues

The conformational properties of protein fragments have been widely studied as models of the earliest initiation events in protein folding. While native-like alpha-helices and beta-turns have been identified, less is known about the factors that underly beta-sheet formation, in particular beta-hairpins, where considerably greater long-range order is required. The N-terminal 20 residue sequence of native ferredoxin I (from the blue-green alga Aphanothece sacrum) forms a beta-hairpin in the native structure and has been studied in isolation by NMR and CD spectroscopy. Local native-like interactions alone are unable to stabilize significantly a folded conformation of the 20-residue fragment in purely aqueous solution. However, we show that the addition of low levels of organic co-solvents promotes formation of native-like beta-hairpin structure. The results suggest an intrinsic propensity of the peptide to form a native-like beta-hairpin structure, and that the organic co-solvent acts in lieu of the stabilizing influence of tertiary interactions (probably hydrophobic contacts) which occur in the folding of the complete ferredoxin sequence. The structure of the isolated hairpin, including the native-like register of interstrand hydrogen bonding interactions, appears to be determined entirely by the amino acid sequence. The solvent conditions employed have enabled this intrinsic property to be established.     

The effects of anger and relaxation forms of in vivo emotive imagery on pain tolerance.

To examine the effects of "in vivo' emotive imagery on pain tolerance, 40 male and 40 female college students were stratified on sex and assigned randomly to no-treatment control, neutral imagery, anger emotive imagery, or relaxation emotive imagery conditions during which they were asked to immerse their hands in ice water (0 °C) for as long as possible. A sex by treatment analysis of variance followed by Tukey post hoc comparisons showed that anger "in vivo' emotive imagery was significantly more effective for females than no-treatment control procedures. No significant differences were noted in males. (French summary) (26 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Context effects on semantic domains as seen in analogy solution.

Three experiments investigated the processing of categorical information in context. Exp 1 used multidimensional scaling techniques to identify some common and unique dimensions for a given set of occupational terms in 3 different contexts. The results of Exp 2 indicate that these context-specific representations (as opposed to the general one) were used in the solution of word analogies. The results of Exp 2 also suggest that Ss solve these word analogies by means of heuristics rather than algorithmic rules. The results of Exp 3 support this conclusion. These findings are discussed in terms of the processing of context-dependent conceptual representations. (PsycINFO Database Record (c) 2010 APA, all rights reserved)