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At least 181 records · Page 10Linked to original sources
PubMed1983

Macrophage-mediated cytostatic activity blocks lymphoblast cell cycle progression independently in both G1 phase and S phase.

Recent work has shown that macrophage-mediated cytostatic activity inhibits cell cycle traverse in G1 and/or S phase of the cell cycle without affecting late S, G2, or M phases. The present report is directed at distinguishing between such cytostatic effects on G1 phase or S phase using the accumulation of DNA polymerase alpha as a marker of G1 to S phase transition. Quiescent lymphocytes stimulated with concanavalin A undergo a semisynchronous progression from G0 to G1 to S phase with a dramatic increase in DNA polymerase alpha activity between 20 and 30 hr after stimulation. This increase in enzyme activity was inhibited, as was the accumulation of DNA, when such cells were cocultured with activated murine peritoneal macrophages during this time interval. However, if mitogen-stimulated lymphocytes were enriched for S-phase cells by centrifugal elutriation and cocultured with activated macrophages for 4-6 hr, DNA synthesis was inhibited but the already elevated DNA-polymerase activity was unaffected. Similar results were obtained when a virally transformed lymphoma cell line was substituted as the target cell in this assay. These results show that both G1 and S phase of the cycle are inhibited and suggest that inhibition of progression through the different phases may be accomplished by at least two distinct mechanisms.

Animals↗
PubMed1992

The inverted hexagonal phase is more sensitive to hydroperoxidation than the multilamellar phase in phosphatidylcholine and phosphatidylethanolamine aqueous dispersions.

The effect of phase behaviour (hexagonal II phase and lamellar phase) on the peroxidation of membrane phospholipids has been investigated in dilinoleoyl phosphatidylcholine (DLPC)/dilinoleoyl phosphatidylethanolamine (DLPE) aqueous dispersions. Peroxidation was initiated with a water-soluble radical inducer 2,2'-azobis (2-amidino-propane) dihydrochloride (AAPN). The phospholipid morphology was monitored by 31P-nuclear magnetic resonance (NMR). Phospholipid hydroperoxides (PCOOH and PEOOH) were determined by chemiluminescence high-performance liquid chromatography (CL-HPLC). In pH-induced phase transition systems, DLPE in the bilayer state was much less oxidized than in the hexagonal II state. In composition-induced phase transition systems, the formation of total hydroperoxides and the consumption of alpha-tocopherol in the hexagonal II phase were greater than in the bilayer phase. These data suggest that the hexagonal II phase is more sensitive to hydroperoxidation than the bilayer phase in phospholipid aqueous dispersions.

Chromatography, High Pressure Liquid↗
PubMed1993

Reversed-phase liquid chromatography with microspherical octadecyl-zirconia bonded stationary phases.

Microspherical zirconia particles were synthesized and surface modified with octadecylsilane compounds for reversed-phase high-performance liquid chromatography. Monomeric and "polymeric" octadecyl-zirconia bonded stationary phases were obtained by reacting the support with octadecyldimethylchlorosilane or octadecyltrichlorosilane, respectively. The surface coverage of the zirconia-based stationary phases with octadecyl functions was approximately the same as that of octadecyl-silica sorbents. These phases were evaluated in terms of reversed-phase chromatographic properties with non-polar, slightly polar and ionic species over a wide range of mobile phase composition and pH. Monomeric octadecyl-zirconia with end-capping exhibited some metallic interactions with both basic and acidic solutes, but these interactions were greatly reduced in the presence of competing agents (e.g., tartrate ions) in the mobile phase. The "polymeric" octadecyl-zirconia sorbents exhibited higher retention than the monomeric ones with the various solutes investigated, and their residual absorptivities toward acidic solutes were much lower. The retention of non-polar and slightly polar aromatic compounds was quasi-homoenergetic on both types of octadecyl-zirconia stationary phases. Stability studies conducted at extreme pH conditions (pH 2.0 and pH 12.0), have shown that "polymeric" octadecyl-zirconia sorbents are more stable than their monomeric counterparts. These stationary phases were quite useful in the separation of polycyclic aromatic hydrocarbons, alkylbenzene and phenyl alkylalcohol homologous series, oligosaccharides, dansyl-amino acids, peptides and proteins.

Amino Acid Sequence↗
PubMed1992

Interneuronal interaction between members of quadrature phase and anti-phase pairs in the cat's visual cortex.

Interactions between adjacent simple cells recorded simultaneously from the same microelectrode placement were studied by correlational analysis. The receptive fields of pairs of such cells exhibit either 90 degrees (quadrature phase) or 180 degrees (anti-phase) phase relationships. We now show that the majority of quadrature phase pair members do not receive common input from the immediately precedent stage along the visual pathway, nor do these cells interact with each other. The anti-phase pairs show relatively strong mutual inhibition. These results suggest that each of the physically adjacent phase-related simple cells receives excitatory input from a distinct group of pre-cortical cells, and that mutual inhibitions between members of anti-phase pairs are used to construct the inhibitory subzones of these cells. We propose a model which incorporates these new results and provides a parsimonious explanation for the construction of both quadrature phase and anti-phase pairs.

Animals↗
PubMed1988

Effect of rapidity of phase separation on the efficiency of cell fractionation by partitioning in aqueous two-phase systems.

Partitioning in two-polymer aqueous phase systems is an established method for the separation, purification and characterization of biomaterials. Because of the relatively slow settling rates of these phases, a consequence of the slight difference in density between them, effort has been directed to speeding up phase separation by various means (e.g., the development of a thin-layer countercurrent distribution apparatus). This has resulted in the more rapid processing of materials. Unlike soluble materials, biological particulates (e.g., cells) generally partition between one of the bulk phases and the interface. The mechanism of cell partitioning involves cell-specific adsorption to droplets of one phase suspended in the other, subsequent to phase mixing, and the delivery of adsorbed cells to the bulk interface as the droplets settle. In this communication we show, using erythrocytes as a model, that speeding up phase separation is counterproductive when partitioning cells and results in reduced efficiency of their separation or subfractionation. The most likely reason for this result is that increasing the speed of phase settling removes the droplets of one phase suspended in the other more rapidly than cells can attach to them, thereby interfering with the mechanism whereby cells partition.

Animals↗
PubMed1995

Ab initio phase determination and phase extension using non-crystallographic symmetry.

Non-crystallographic symmetry (NCS) can be used to improve, extend or find ab initio phases to be associated with a set of observed structure amplitudes, resulting in an interpretable electron-density map. The simplest application is merely to improve the accuracy of the phases by cyclically averaging the electron density, Fourier back-transformation of the modified map, and recomputing a new map with the newly found phases. The first sophistication of this procedure is to phase extend, in successive small steps, the currently available phase information to higher resolution, where only observed amplitudes were previously available. A further sophistication is to initiate the phase extension from very low resolution where a simple geometric model, or an electron microscope image, would be consistent with the chosen resolution. A number of recent examples of virus structure determination exist where such ab initio phasing was successful. The ultimate ab initio phase determination would be to extend phases given only an estimate of the F(000) term.

Crystallography, X-Ray↗
PubMed1995

Phase diagram of soybean phosphatidylcholine-diacylglycerol-water studied by x-ray diffraction and 31P- and pulsed field gradient 1H-NMR: evidence for reversed micelles in the cubic phase.

The phase equilibria of the system soybean phosphatidylcholine, diacylglycerol, and water has been determined using a combination of classical methods together with x-ray diffraction and NMR techniques. In particular, the extent of the phase regions of the lamellar, the reversed hexagonal, and the cubic phases have been determined. By pulsed field gradient 1H-NMR, the diffusion coefficients of all three components in a cubic phase composed of soybean phosphatidylcholine, diacylglycerol, and heavy water have been determined at 25 and 59 degrees C and also for the corresponding cubic phase composed of the chemically more well defined synthetic components 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC), 1,2-dioleoylglycerol (DOG), and heavy water. The extension of the phase region of the cubic phase did not seem to change appreciably for the two ternary systems studied. The translational diffusion coefficient of DOPC in this cubic phase is more than an order of magnitude smaller (3 x 10(-13) m2 s-1, 59 degrees C) than the lateral diffusion coefficient of DOPC in an oriented lipid bilayer (5 x 10(-12) m2 s-1, 35 degrees C), whereas the diffusion coefficients of water and DOG were found to be about two orders of magnitude larger than DOPC at 59 degrees C. It is concluded that the cubic phase is built built up of closed reversed micelles in accordance with the suggestion from previous x-ray diffraction studies.

Diglycerides↗
PubMed1997

Influence of the intrinsic membrane protein bacteriorhodopsin on gel-phase domain topology in two-component phase-separated bilayers.

We have investigated the effect of the intrinsic membrane protein bacteriorhodopsin of Halobacterium halobium on the lateral organization of the lipid phase structure in the coexistence region of an equimolar mixture of dimyristoylphos-phatidylcholine and distearoylphosphatidylcholine. The fluorescence recovery after photobleaching (FRAP) technique was used to monitor the diffusion of both a lipid analog (N-(7-nitrobenzoxa-2,3-diazol-4-yl)-dimyristoylphosphatidyle thanolamine, NBD-DMPE) and fluorescein-labeled bacteriorhodopsin (Fl-BR). In the presence of bacteriorhodopsin, the mobile fractions of the two fluorescent probes display a shift of the percolation threshold toward lower temperatures (larger gel-phase fractions), independent of the protein concentration, from 43 degrees C (without bacteriorhodopsin) to 39 degrees C and 41 degrees C for NBD-DMPE and Fl-BR, respectively. Moreover, in the presence of bacteriorhodopsin, the gel-phase domains are much less efficient in restricting the diffusion of both probes than they are in the absence of the protein in the two-phase coexistence region. Bacteriorhodopsin itself, however, obstructs diffusion of NBD-DMPE and Fl-BR to about the same extent in the fluid phase of the two-phase region as it does in the homogeneous fluid phase. These observations suggest that 1) the protein induces the formation of much larger and/or more centrosymmetrical gel-phase domains than those formed in its absence, and 2) bacteriorhodopsin partitions almost equally between the coexisting fluid and gel phases. Although the molecular mechanisms involved are not clear, this phenomenon is fully consistent with the effect of the transmembrane peptide pOmpA of Escherichia coli investigated by electron spin resonance in the same lipid system.

Affinity Labels↗
PubMed2001

Regulation of grasping forces during bimanual in-phase and anti-phase coordination.

When a hand-held object is moved, grip force is adapted in an anticipatory manner to load force due to a dynamic coupling between both forces. The present study addressed the issue of grip-load force regulation when moving rhythmically two hand-held objects in the vertical dimension, and more specifically the divergence of force control when performing according to the in-phase versus anti-phase mode. Results revealed that grip-load force ratio profiles were similar in both bimanual conditions. That is, force ratio was not constant throughout the movement cycles but followed a fairly regular pattern with maxima and minima, attained at upward and downward hand positions, respectively. However, anti-phase patterns showed an increased maximum grip-load force ratio as compared to in-phase patterns, whereas the latter did not differ from unimanual movements. The magnification of maximum force ratio during anti-phase movements suggests that rescaling occurred. This is likely due to the complexity of the anti-phase mode that necessitates increased monitoring and attention relative to the other performance conditions, creating a coordinative situation that imposes an additional degree of uncertainty. Therefore, the safety margin is amplified during anti-phase movements, probably as a strategy to prevent a potential destabilization of the grip during an asymmetrical load condition. Accordingly, these findings also demonstrate that grip-load force regulation is more proficiently controlled during bimanual in-phase than anti-phase movements. Herewith, the data add content to earlier work illustrating kinematic dissimilarities between both coordination modes.

Adult↗
PubMed2003

Head movements destabilize cyclical in-phase but not anti-phase homologous limb coordination in humans.

The present study addressed the role of head movements in the coordination of the homologous upper or lower limbs in supine normal subjects. Consistent with previous research, in-phase mirror symmetrical movements were performed more accurately and consistently than anti-phase movements. However, inclusion of head movements destabilized in-phase but not anti-phase homologous limb coordination, in contrast to previous work demonstrating a higher vulnerability of anti-phase than in-phase coordination to various experimental perturbations. It was observed that the head moved in the same direction as the limbs during anti- but not during in-phase coordination. Furthermore, the interlimb patterns also affected the head rotations that were lower in spatiotemporal consistency and less consistently coupled with the limbs during in-phase than during anti-phase coordination. These findings provide new insights into the coalition of egocentric and allocentric constraints during interlimb coordination.

Adult↗
PubMed1992

Temperature dependence of retention in reversed-phase liquid chromatography. 1. Stationary-phase considerations.

The retention mechanism in reversed-phase liquid chromatography (RPLC) has been investigated by examining the temperature dependence of retention, with emphasis on the role of the stationary phase in the retention process. Both chromatographic temperature studies and differential scanning calorimetry were used to examine the role of alkyl chain bonding density on the retention mechanism in RPLC. Phase transitions of reversed-phase stationary phases were observed at bonding densities greater than 2.84 mumol/m2. Thermodynamic constants for the transfer of a solute from the mobile phase to the stationary phase (delta H degrees and delta S degrees) were calculated for low bonding density columns, and comparison of these values to previously reported values for the partitioning of a nonpolar solute from the bulk organic liquid to water indicated that the chromatographic retention process is not well-modeled by bulk-phase oil-water partitioning processes. In addition, this data showed that the entropic contribution to retention becomes more significant with respect to the enthalpic contribution as the stationary-phase bonding density is increased, providing additional support that partitioning, rather than adsorption, is the relevant model of retention.

Chromatography, High Pressure Liquid↗
PubMed1995

Bioavailability estimation by reversed-phase liquid chromatography: high bonding density C-18 phases for modeling biopartitioning processes.

There have been many attempts to estimate biological activity with either 1-octanol/water partition coefficients or chromatographic retention parameters. Bulk phases may not be appropriate, however, for modeling a partitioning process in an interphase such as biological membranes. Chromatographic stationary phases can be argued as having structure similar to a membrane because of chain organization; however, the density of the grafted stationary-phase chains in commercially available stationary phases is much too low to provide a suitable model. We have previously developed a new scheme for derivatizing silica surfaces that produces stationary phases of significantly higher chain density than traditional methods. Investigation of the molecular mechanism and thermodynamics of solute partitioning into the different phases has shown that densely bonded reversed-phase stationary phases mimic partitioning to a biomembrane better than does bulk-phase octanol. Here we report chromatographic retention for pesticides, PAHs, and barbiturates using a C-18 column with high alkyl chain density, and in all cases, correlations of log k'w with bioavailability are equivalent to or better than correlations of bioavailability with the octanol/water partition coefficient.

Animals↗
PubMed2002

Structure-function relationships in high-density octadecylsilane stationary phases by Raman spectroscopy. 2. Effect of common mobile-phase solvents.

Raman spectroscopy is used to examine the effects of solvent, temperature, and surface grafting method (surface or solution polymerized) on alkyl chain rotational and conformational order in a series of high-density octadecylsilane stationary phases ranging in surface coverage from 3.09 to 6.45 micromol/m2. Rotational and conformational order is assessed using the intensity ratio of the antisymmetric to symmetric v(CH2) modes as well as the frequency at which these Raman bands are observed. Solvents studied include perdeuterated hexane, toluene, chloroform, tetrahydrofuran, benzene, methanol, acetone, acetonitrile, and water. Stationary-phase order was investigated at temperatures between 258 and 323 K. Alkyl chain rotational and conformational order, and hence, solvation of the stationary phase, is dependent on solvent parameters (polarity, size, etc.), temperature, and stationary-phase properties (polymerization method and surface coverage). Information on stationary-phase conformational order allows solvent-stationary-phase interactions to be described in terms of a combination of adsorption and partitioning models for reversed-phase liquid chromatography. Finally, a distinct interplay between solvent- and temperature-induced ordering of these stationary phases is documented that is also a function of solvent and stationary-phase properties.

Molecular Conformation↗
PubMedDate not supplied

Isotropic-nematic phase equilibrium and phase separation of kappa-carrageenan in aqueous salt solution: experimental and theoretical approaches.

The behavior of chiral-nematic and isotropic phases of helical kappa-carrageenan in aqueous solution of sodium iodide was compared with that of the anisotropic biphasic phase that contains both these phases. On the basis of birefringence, rheology, chemical analysis, average molecular weight, and polydispersity index measurements, we derived a number of characteristic differences as well as similarities between these phases, over a range of polysaccharide concentrations obtained by the dilution of each phase. For example, we assessed the critical concentration of an isotropic-anisotropic transition (C(i)), the temperature of the anisotropic-isotropic phase shift during thermal heating-cooling cycles, and the viscosity changes due to the phase shift and due to the diminishing of the helical conformation. We also demonstrated how the different phases and their dilutions behave under the effect of shear and frequency of oscillation and how the viscoelastic properties vary in each phase and discussed the isotropic and anisotropic liquid crystal controlling behavior mechanisms. From a theoretical point of view, we propose to combine the wormlike chain model for semiflexible polyelectrolytes interacting via both hard-core and electrostatic repulsion to assess the concentration of isotropic-nematic transition, to assess the coexistence concentration range, and to determine the effects of charge by applying the effective diameter and a twisting effect.

Anisotropy↗
PubMedDate not supplied

An on-line phase measurement system for quality assurance of the BSD 2000. Part II: results of the phase measurement system.

Phase constancy and accuracy are significant for regional hyperthermia with phased array radiofrequency hyperthermia systems. They are both necessary for a precise target steering in therapy. For the BSD 2000 system (BSD Medical Corp. Salt Lake City, Utah, USA), the phase values of all channels are checked with a self-developed automatic on-line phase measurement system. On different days the phases are measured under identical conditions, where the output paths are cut off with 50 ohm dummy loads to suppress the influence of the radiation conditions of the antennae on the measurement values. The results show how the phase values of the four channels change in the first 30 min and from day to day. During this time interval after the start the phases drop down by up to 15 degrees. For the time later changes are very slight and the differences from day to day are negligible. The phase shift that occurs in the first 30 min is as high as a change of the target point by 1 cm. Earlier switching on of the amplifiers prevents this shift occurring during the treatment. The measurement system provides a good tool for determination of phase accuracy and is easy to realize.

Humans↗
PubMed2000

Characterizing the selectivity of stationary phases and organic modifiers in reversed-phase high-performance liquid chromatographic systems by a general solvation equation using gradient elution.

Retention data for a set of 69 compounds using rapid gradient elution are obtained on a wide range of reversed-phase stationary phases and organic modifiers. The chromatographic stationary phases studied are Inertsil (IN)-ODS, pentafluorophenyl, fluoro-octyl, n-propylcyano, Polymer (PLRP-S 100), and hexylphenyl. The organic solvent modifiers are 2,2,2-trifluoroethanol (TFE); 1,1,1,3,3,3-hexafluoropropan-2-ol (HFIP); isopropanol; methanol (MeOH); acetonitrile (AcN); tetrahydrofuran; 1,4-dioxane; N,N-dimethylformamide; and mixed solvents of dimethylsulfoxide (DMSO) with AcN and DMSO with MeOH (1:1). A total of 25 chromatographic systems are analyzed using a solvation equation. In general, most of the systems give reasonable statistics. The selectivity of the reversed phase-high-performance liquid chromatographic (HPLC) systems with respect to the solute's dipolarity-polarity, hydrogen-bond acidity, and basicity are reflected in correspondingly large coefficients in the solvation equation. We wanted to find the most orthogonal HPLC systems, showing the highest possible selectivity difference in order to derive molecular descriptors using the gradient retention times of a compound. We selected eight chromatographic systems that have a large range of coefficients of interest (s, a, and b) similar to those found in water-solvent partitions used previously to derive molecular descriptors. The systems selected are IN-ODS phases with AcN, MeOH, TFE, and HFIP as mobile phase, PLRP-S 100 phase with AcN, propylcyano phase with AcN and MeOH, and fluorooctyl phase with TFE. Using the retention data obtained for a compound in the selected chromatographic systems, we can estimate the molecular descriptors with the faster and simpler gradient elution method.

Journal Article↗
PubMed2003

Chromatographic behavior of ion pair enantiomers of dansyl leucine cyclohexylammonium salt on a beta-cyclodextrin stationary phase and the effect of a competitive-binding mobile phase additive.

The separation of dansyl leucine enantiomers on a beta-cyclodextrin stationary phase is significantly complicated by the association of the amino acid with its cyclohexylammonium counter ion, in a mobile phase of 80:20 (v/v) methanol-water. This produces very unusual chromatography, with two partially superimposed peaks observed for each enantiomer at lower column temperatures. The peak shape is attributed to the irreversible, oncolumn conversion of the ion pair (I) to the free, protonated (neutral) dansyl amino acid (II+H). Increasing the ionic strength of the mobile phase greatly improves the chromatography by transforming the solute species to enantiomers of II (the anionic, free amino acid). Van't Hoff plots are constructed for both species I and II (under different mobile phase conditions) to provide thermodynamic insight into the major enantioselective driving forces of separation. The chiral discrimination of the stationary phase is found to be primarily enthalpically driven for both solutes. Finally, 1-adamantanecarboxylic acid (ACA) is investigated as a solute-competitive mobile phase additive to intentionally block the hydrophobic cyclodextrin cavities on the stationary phase. By varying the concentration of ACA additive in the mobile phase, control over the retention and chiral recognition of the stationary phase is demonstrated.

Journal Article↗
PubMed1997

Expression of different molecular mass forms of inhibin in atretic and nonatretic follicles during the early luteal phase and altrenogest-synchronized follicular phase in pigs.

This experiment characterized changes in amounts and proportions of different molecular forms of inhibin in porcine follicular fluid as related to stage of follicular development. Thirty-seven follicles (2-4 per pig) were dissected from 12 pigs during early luteal phase of the estrous cycle on Days 5, 6, and 7 of the estrous cycle, whereas 34 follicles (2-4 per pig) were dissected from 11 pigs on Days 1, 3, 5, and 7 of a follicular phase synchronized by altrenogest. Follicles were designated atretic if incidence of apoptotic granulosa cells was > or = 10% as determined by DNA fluorescence flow cytometry. Porcine follicular fluid was fractionated on 12% SDS-PAGE gels under non-reducing conditions and electroblotted to Immobilin P membranes. Inhibin forms were detected by immunoblot analysis using a mink anti-bovine inhibin alpha C1-26 gly.tyr antiserum and quantified. Immunoblots detected seven bands corresponding to inhibin forms of 44, 49, 58, 69, 121, 227, and > 227 kDa in > 91% of porcine follicular fluid samples. Three additional forms of 27, 29, and 32 kDa were detectable in only 52%, 64%, and 48% of samples, respectively. Forms > or = 69 kDa represented 83% of total inhibin immunoblot activity. The 121-kDa form was most abundant, with 39% of the total immunoblot activity in nonatretic follicles. The proportions of individual forms and total immunoblot activity pooled over days did not differ between early luteal and follicular phase follicles. Total inhibin immunoblot activity was 59% less in atretic than in nonatretic follicles. Amounts of the 44-, 49-, 69-, 121-, and 227-kDa forms were 50-80% lower (p < or = 0.05) in atretic than in nonatretic follicles. Total inhibin immunoblot activity in nonatretic follicles decreased (p < or = 0.05) by 60% during the early luteal phase but did not change significantly during the follicular phase. In nonatretic follicles, the 121-kDa form decreased (p < 0.05) during the early luteal and follicular phases. During the early luteal phase, amounts of the other forms did not change, whereas during the follicular phase the 44-kDa form increased (p < 0.05) 10-fold. In atretic follicles, neither amount nor proportion of inhibin forms differed among days. We conclude that follicular production and/or intracellular processing of inhibin dimer and/or inhibin alpha subunits changes during different phases of follicular development, supporting the notion of physiological roles for these peptides.

Androstenedione↗