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At least 793 records · Page 44Linked to original sources
PubMed1981

Differences in rearrangements of H1 and H5 in chicken erythrocyte chromatin.

H1 can rearrange in chicken erythrocyte polynucleosomes in 80 mM NaCl buffers. These rearrangements have been studied by sedimentation analysis. H1 redistributes between polynucleosomes as well as between polynucleosomes and monosomes. In these rearrangements H1 molecules move to free DNA sites. In contrast to H1, the chicken erythrocyte specific lysine-rich histone H5 does not show any of these dynamic properties. This difference in mobility of H1 and H5 also manifests itself in the selective extraction of H1 from H1, H5 containing polynucleosomes by the cation-exchange resin AG 50W-X2 at 80 mM NaCl.

Animals↗
PubMed1981

Evidence for a species of nuclear actin distinct from cytoplasmic and muscles actins.

Nuclear actin (protein BJ) has been isolated from the chromatin of Novikoff hepatoma ascites cells and purified to homogeneity by selective extraction, Sepharose CL-6B chromatography, and preparative polyacrylamide gel electrophoresis. A comparison of nuclear and cytoplasmic actins from Novikoff hepatoma cells and rabbit muscle actin was made by amino acid analysis, isoelectric focusing/sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and two-dimensional peptide mapping procedures. By these criteria, all of the proteins compared are actins, but each is chemically distinct. It was concluded, therefore, that nuclear actin is similar to, but not identical with, cytoplasmic actin isolated from Novikoff hepatoma cells. A striking similarity in peptide charge and migration as shown by peptide map analysis was observed for nuclear and rabbit skeletal muscle actins. This may indicate that nuclear actin has the capacity for contractile function. In addition, the actins synthesized in Novikoff hepatoma cells may results from more than two structural genes.

Actins↗
PubMed1981

Protein involvement in structural transition of erythrocyte ghosts. Use of thermal gel analysis to detect protein aggregation.

In this study, it is shown that systematic temperature-induced protein aggregation occurs on the erythrocyte membrane by intermolecular disulfide bond formation. Specific protein bands disappear from acrylamide gel profiles over rather narrow temperature regions. The aggregation appears to be the result of irreversible structural transitions of the membrane, which can be seen in a sensitive scanning calorimeter. When this method of thermal gel analysis is used, the results suggest that spectrin is a participant in the A transition, that bands 2.1, 4.1, and 4.2 and the cytoplasma portion of 3 are involved in the B transition, and that the transmembrane portion of band 3 may undergo changes in the C transition, previously shown to occur in the anion transport domain of the membrane. The aggregation of specific proteins in the narrow temperature region of these transitions persists as the transitions are moved around on the temperature axis by varying solution conditions. The assignment of particular proteins to specific transitions is reinforced by selective extraction of membrane proteins. Large variations in both the calorimetry and the aggregation pattern occur as salt concentration is increased from 77 mosm to 310 mosm, which is manifested in the splitting of the B transition into two separate transitions, B1 and B2. It is speculated that this occurs as the result of a structural change which may involve components of the cytoskeletal network.

Calorimetry↗
PubMed2005

Total chemical synthesis of human psoriasin by native chemical ligation.

Human psoriasin (S100A7), a member of the S100 family of calcium-binding proteins, is richly expressed in keratinocytes of patients suffering from psoriasis. To date, the exact physiological function of psoriasin abundant in many human cell types remains unclear. A recent report by Schröder and colleagues suggests that psoriasin, purified from human stratum corneum extracts, selectively kills Escherichia coli by sequestering Zn(2+) ions essential for bacterial growth, indicative of an important role in innate immune defense against microbial infection. We chemically synthesized the N-terminally acetylated psoriasin of 100 amino acid residues using solid phase peptide synthesis in combination with native chemical ligation. More than 140 mg of highly pure and correctly folded synthetic psoriasin was obtained from a single synthesis on a 0.25 mmol scale. Analysis of synthetic psoriasin by size exclusion chromatography showed that the protein forms a homodimer in solution. Circular dichroism analysis indicated that the alpha-helicity of psoriasin increases by more than 20% in the presence of CaCl(2) or ZnCl(2), suggesting a metal ion binding induced conformational change. Circular dichroism based titration further established that the synthetic protein binds two Ca(2+) and two Zn(2+) ions per dimer, in agreement with the published structural findings. Importantly, the ability of the synthetic protein to kill E. coli and the inhibition of the killing by ZnCl(2) is comparable to that of psoriasin isolated from its natural source. The robust synthetic access to large quantities of human psoriasin should facilitate studies of its biological functions as well as its mode of action.

Amino Acid Sequence↗
PubMedDate not supplied

Screening of a combinatorial library of synthetic polyamines displaying selectivity in multiple ion-pairing interactions with model polyanionic compounds in aqueous organic solutions.

The biological activity of natural polyamines is due in large part to their ability to form ion-pairing interactions with polyanionic biomolecules, such as proteins, oligonucleotides, and sulfated oligosaccharides. Unfortunately, the diversity of biogenic polyamines is compromised by their limitation to only just a few internitrogen spacers. As a proof-of-principle study, a synthetic split-pool library of linear triamines was screened in an on-bead assay against a selection of model trisulfonated azo dyes (1, 2, and 3) and a short glutamate-rich nonameric peptide (4) to demonstrate its use in the discovery of selective ligands via multivalent ion pairing. From screening a 196-membered split-pool library against the dyes in aqueous organic solutions, with or without spermidine as competing ligand, it was found that the most frequent residues possessed internitrogen distances that were very similar to the sulfonate distances on the dyes. The results from these screening assays were used in the design of two polyamine sequences (8, 8Aoc(R)-8Aoc(R), and 12, 2Acc(R)-epsilonAhx(R)) for follow-up studies in solution phase. These triamines demonstrated the same selectively toward dyes 2 and 3 as observed by the solid-phase approach. In addition, resin-supported triamines, synthesized as discrete compounds, were able to selectively extract either dye 2 or 3 from a mixture of the two, further verifying the observations made from the library screening efforts. With peptide 4, containing three glutamate residues, a preference was found for rather long residues (12 and 8 carbons long), which is suggestive of a linear peptide, rather than a helical motif under the conditions of the screening.

Azo Compounds↗
PubMed2005

Development and application of an electron spin resonance spectrometry method for the determination of oxygen free radical formation by particulate matter.

Exposure to increased levels of ambient particulate matter (PM) are associated with several health effects, including cardiopulmonary diseases. The formation of reactive oxygen species (ROS) is thought to play an important role in the induction of these health effects. To quantify the ROS generating capacityof PM,we developed an improved electron spin resonance (ESR) spectrometry-based method. ROS formation was measured directly on PM-containing filters, thereby avoiding the selective extraction of components and loss of material or reactivity, which is likely to occur during filter extraction. Also, ascorbic acid was added to stimulate ROS formation. This method was applied to PM10 samples originating from different sources. The radical generating capacity of PM10 from both gasoline and diesel engine exhaust was significantly higher as compared to that of PM10 from ambient or indoor air. Furthermore, in urban PM10 and PM2.5, ROS-generating capacity significantly correlated with concentrations of polycyclic aromatic hydrocarbon content and particular transition metals. This indicates thatthis improved ESR method may be a valuable tool for evaluating the relationship between ROS formation by PM and the adverse health effects associated with this type of air pollution.

Electron Spin Resonance Spectroscopy↗
PubMed2005

Solubility, complex formation, and redox reactions in the Tl2O3-HCN/CN(-)-H2O system. Crystal structures of the cyano compounds Tl(CN)3.H2O, Na[Tl(CN)4].3H2O, K[Tl(CN)4], and Tl(I)[Tl(III)(CN)4] and of Tl(I)2C2O4.

Thallium(III) oxide can be dissolved in water in the presence of strongly complexing cyanide ions. Tl(III) is leached from its oxide both by aqueous solutions of hydrogen cyanide and by alkali-metal cyanides. The dominating cyano complex of thallium(III) obtained by dissolution of Tl2O3 in HCN is [Tl(CN)3(aq)] as shown by 205Tl NMR. The Tl(CN)3 species has been selectively extracted into diethyl ether from aqueous solution with the ratio CN-/Tl(III) = 3. When aqueous solutions of the MCN (M = Na+, K+) salts are used to dissolve thallium(III) oxide, the equilibrium in liquid phase is fully shifted to the [Tl(CN)4]- complex. The Tl(CN)3 and Tl(CN)4- species have for the first time been synthesized in the solid state as Tl(CN)3.H2O (1), M[Tl(CN)4] (M = Tl (2) and K (3)), and Na[Tl(CN)4].3H2O (4) salts, and their structures have been determined by single-crystal X-ray diffraction. In the crystal structure of 1, the thallium(III) ion has a trigonal bipyramidal coordination with three cyanide ions in the equatorial plane, while an oxygen atom of the water molecule and a nitrogen atom from a cyanide ligand, attached to a neighboring thallium complex, form a linear O-Tl-N fragment. In the three compounds of the tetracyano-thallium(III) complex, 2-4, the [Tl(CN)4]- unit has a distorted tetrahedral geometry. Along with the acidic leaching (enhanced by Tl(III)-CN- complex formation), an effective reductive dissolution of the thallium(III) oxide can also take place in the Tl2O3-HCN-H2O system yielding thallium(I), while hydrogen cyanide is oxidized to cyanogen. The latter is hydrolyzed in aqueous solution giving rise to a number of products including (CONH2)2, NCO-, and NH4+ detected by 14N NMR. The crystalline compounds, Tl(I)[Tl(III)(CN)4], Tl(I)2C2O4, and (CONH2)2, have been obtained as products of the redox reactions in the system.

Journal Article↗
PubMed1997

Self-Assembly of Homochiral Double Helix and Side-by-Side Helix Conformers of Double-Stranded Disilver(I)- and Digold(I)-Tetra(tertiary phosphine) Helicates.

The enantiomers of the (R,R)-(+/-) diastereomer of the chelating C(2)-tetra(tertiary phosphine) (R,R)-(+/-)-1,1,4,7,10,10-hexaphenyl-1,4,7,10-tetraphosphadecane, (R,R)-(+/-)/(R,S)-1, spontaneously self-assemble into homochiral double-stranded disilver(I) and digold(I) helicates of the type [M(2)(tetraphos)(2)]X(2) upon reaction with appropriate silver(I) and gold(I) salts. The corresponding copper(I) complex is mononuclear. Crystal and molecular structures of Delta-(-)-[Cu{(R,R)-1}]PF(6).EtOH, Lambda-(-)-[Ag(2){(R,R)-1}(2)](PF(6))(2), and Lambda-(-)-[Au(2){(R,R)-1}(2)](PF(6))(2).CH(2)Cl(2) are reported. The structure determinations on the silver and gold complexes are the first to be performed on enantiomerically pure dimetal helicates with chiral ligands. The dinuclear silver complex crystallizes with one molecule each of the left-handed (Lambda) D(2)-double helix and C(2)-side-by-side helix conformers of the cation and associated anions in each unit cell, whereas crystals of the analogous gold complex contain only the side-by-side helix and associated anions. The absolute configuration(s) of the metal stereocenter(s) in each complex is S. Conductance measurements in acetonitrile indicated considerable rearrangement of the mononuclear copper complex into the dinuclear helicate complex, whereas the silver and gold complexes conducted as di-univalent salts under similar conditions. Energy minimization calculations of the structures of the disilver complex cation with use of the program SPARTAN 3.0 predicted the structures observed with considerable accuracy, especially the conformations of the chiral central ten-membered ring in the complex and the relationship of the helicity of this ring to the stereoselective formation of the double helix and side-by-side helix structures. The resolution of (R,R)-(+/-)-1 is the first on a tetra(tertiary phosphine). The more-soluble (R,R)-(+/-) form of the ligand was separated in high yield from the less-soluble (R,S) form by selective extraction with tetrahydrofuran, whereupon it was resolved by the method of metal complexation with the readily prepared homochiral complex (+)-di(&mgr;-chloro)bis[(R)-1-[1-(dimethylamino)ethyl]-2-phenyl-C(2),N]dipalladium(II)-1-dichloromethane, (R)-2.CH(2)Cl(2). The enantiomers of the phosphine were obtained by liberation from the diastereomeric complexes (R(C)),(R(P),R(P))- and (R(C)),(S(P),S(P))-3 (X = PF(6)) and brought to optical purity by crystallization from acetone-ethanol, giving colorless needles having mp 88 degrees C and [alpha](21)(D) +20.5 (c 1.0, CH(2)Cl(2)) (S,S enantiomer) and [alpha](21)(D) -20.5 (c 1.0, CH(2)Cl(2)) (R,R enantiomer). The crystal and molecular structures of (R(C)),(R(P),R(P))-3 (X = PF(6)) have been determined. The complete optical purity of each enantiomer of the tetra(tertiary phosphine) was confirmed in each case by the quantitative repreparation of the diastereomeric palladium complex from which it was liberated.

Journal Article↗
PubMed2003

Reversible electrochemical detection of nonelectroactive polyions.

Selective extraction principles for the recognition of nonelectroactive polyions such as heparin and protamine exist, but the high ionic valency renders the extraction process irreversible. A response principle for the reversible detection of such polyions is proposed here. The extraction of the polyionic analyte to the membrane and its subsequent back-extraction is now controlled electrochemically. The principle is established with a protamine electrode, and excellent stability and reproducibility are demonstrated. This method has important implications for the design of chemical recognition principles for polyionic analytes.

Calibration↗
PubMed2006

Ochratoxin a determination in beer by solid-phase microextraction coupled to liquid chromatography with fluorescence detection: a fast and sensitive method for assessment of noncompliance to legal limits.

A solid-phase microextraction-liquid chromatography-fluorescence detection (SPME-LC-FD) method for the determination of ochratoxin A (OTA) in commercial beer samples was developed for the first time using a 60 microm thick poly(dimethylsiloxane)/divinylbenzene (PDMS/DVB) fiber. The procedure required a very simple sample pretreatment, an isocratic elution, and provides a selective extraction. All of the factors influencing fiber adsorption (extraction time, temperature, pH, and salt addition) and desorption of the analyte (desorption and injection time and desorption solvent mixture composition) have been investigated. The linear range investigated in beer was 0.03-2 ng/mL; within-day and between-days relative standard deviation in beer were 4.3 and 5.9%, respectively. The limit of quantification in spiked beer was 53 pg mL(-)(1), well below all European regulatory levels.

Beer↗
PubMed2000

Potent aroma compounds of two red wine vinegars.

Gas chromatography olfactometry (GCO) was used to determine key aroma compounds of two red wine vinegars. Sensory analysis was performed to choose the best neutralization agent of acetic acid (NaOH or MgO) and to test representativeness of four extracts obtained by different methods (dichloromethane extraction, XAD-2, mixture of XAD-2 and XAD-7, and Extrelut resins extraction). Neutralization with NaOH followed by dichloromethane extraction was selected to extract volatile compounds of vinegars. Key odorant compounds were determined by GCO based on detection frequency with 13 people. In the two red wine vinegars, 13 odors were perceived by at least 70% of the panelists, and 8 compounds among the 13 were identified: acetic acid, 3-methylbutyric acid, 2-phenyl-1-ethanol, 2, 3-butanedione, butyric acid, 2-methylbutyric acid, mixture of 2- and 3-methyl-1-butanol, and two newly identified compounds in vinegar, 3-hydroxy-2-pentanone and 3-(methylthio)-1-propanal. Quantification of all the volatile compounds was performed by GC-FID, and 10 other compounds were identified for the first time in wine vinegar.

Acetic Acid↗
PubMed2000

Separation of thermostable pectinmethylesterase from marsh grapefruit pulp.

A rapid, ion-exchange method that isolates thermostable pectinmethylesterase (TS-PME) from Marsh grapefruit pulp is presented. TS-PME was selectively extracted with 1 M NaCl and equilibrated at low pH (3.1 +/- 0.04). After dilution to a final concentration of 50 mM acetate buffer, pH 5.5, and 0.1, 0.25, or 0.5 M NaCl, the extract was applied to an ion-exchange column without ammonium sulfate precipitation and dialysis. The percent yield varied from an average of 70% (0.1 M NaCl) to 14% (0.5 M NaCl), with a specific activity of >400 U/mg protein in the latter sample. TS-PME activity of some column fractions varied compared with crude extracts before column separation. Some fractions lost thermostability after separation if loaded at 0.1 M or 0.25 M NaCl. In extracts that were loaded at 0.5 M NaCl, the TS-PME activity was significantly higher than that observed in the heated crude extracts. Ion-exchange chromatography may have separated an unidentified protective factor in PME fractions.

Carboxylic Ester Hydrolases↗
PubMed2002

Symplostatin 3, a new dolastatin 10 analogue from the marine cyanobacterium Symploca sp. VP452.

Symplostatin 3 (1), a new analogue of dolastatin 10 (2), has been isolated from a tumor selective extract of a Hawaiian variety of the marine cyanobacterium Symploca sp. VP452. Compound 1 differs from 2 only in the C-terminal unit; the dolaphenine unit is substituted by a 3-phenyllactic acid residue. Symplostatin 3 (1) possesses IC(50) values for in vitro cytotoxicity toward human tumor cell lines ranging from 3.9 to 10.3 nM. It disrupts microtubules, but at a higher concentration than 2, correlating with the weaker in vitro cytotoxicity.

Animals↗
PubMed2003

Ionic liquid as a suitable phase for multistep parallel synthesis of an array of isoxazolines.

[reaction: see text]. A parallel array of isoxazoline diamides was prepared using an ionic liquid [bmim][BF4] as the phase where a three-step procedure (Schotten-Baumann, 1,3-dipolar cycloaddition, ester amidation with Me3Al) was carried out. At the end, selective extraction of the final products with diethyl ether allowed simple isolation of the 16 components of the array (Syncore technology).

Journal Article↗
PubMedDate not supplied

The calcium-binding protein calreticulin is covalently modified in rat liver by a reactive metabolite of the inhalation anesthetic halothane.

A general procedure is presented for the isolation of several liver microsomal target proteins of the reactive trifluoroacetyl halide metabolite of halothane. It was found that most of these proteins could be selectively extracted from microsomes with 0.1% sodium deoxycholate and separated into partially purified fractions by DEAE-Sepharose anion-exchange chromatography. Using this method, we describe the isolation and identification of a 63-kDa target protein of halothane in rat liver. Amino acid sequences of the N-terminal and of several internal peptides of the protein, as well as the deduced amino acid sequence of a nearly full-length rat liver cDNA clone of the protein, showed 98% identity with a reported murine cDNA that encodes for calreticulin, a major calcium-binding protein of the lumen of endoplasmic reticulum. Although it remains to be determined what role calreticulin has in the development of halothane hepatitis, this study has shown that calreticulin can be a target of reactive metabolites of xenobiotics.

Amino Acid Sequence↗
PubMed2000

Long-term follow-up of successful orthodontic-periodontal treatment of localized aggressive periodontitis: a case report.

This report describes a case of localized aggressive periodontitis (localized juvenile periodontitis) that was jointly treated with conventional periodontal therapy, selective extractions to eliminate localized areas of vertical bone loss, and orthodontic therapy. A 20-year follow-up is described in this report. The success of periodontal treatment in a case such as this depends on making an accurate diagnosis, providing periodontal treatment to control the disease, and providing regular periodontal maintenance during and after orthodontic treatment.

Journal Article↗
PubMed2000

In vitro neurogenesis by progenitor cells isolated from the adult human hippocampus.

Neurogenesis persists in the adult mammalian hippocampus. To identify and isolate neuronal progenitor cells of the adult human hippocampus, we transfected ventricular zone-free dissociates of surgically-excised dentate gyrus with DNA encoding humanized green fluorescent protein (hGFP), placed under the control of either the nestin enhancer (E/nestin) or the Talpha1 tubulin promoter (P/Talpha1), two regulatory regions that direct transcription in neural progenitor cells. The resultant P/Talpha1:hGFP+ and E/nestin:enhanced (E)GFP+ cells expressed betaIII-tubulin or microtubule-associated protein-2; many incorporated bromodeoxyuridine, indicating their genesis in vitro. Using fluorescence-activated cell sorting, the E/nestin:EGFP+ and P/Talpha1:hGFP+ cells were isolated to near purity, and matured antigenically and physiologically as neurons. Thus, the adult human hippocampus contains mitotically competent neuronal progenitors that can be selectively extracted. The isolation of these cells may provide a cellular substrate for re-populating the damaged or degenerated adult hippocampus.

Adult↗
PubMed2004

Grain boundaries as reservoirs of incompatible elements in the Earth's mantle.

The concentrations and locations of elements that strongly partition into the fluid phase in rocks provide essential constraints on geochemical and geodynamical processes in Earth's interior. A fundamental question remains, however, as to where these incompatible elements reside before formation of the fluid phase. Here we show that partitioning of calcium between the grain interiors and grain boundaries of olivine in natural and synthetic olivine-rich aggregates follows a thermodynamic model for equilibrium grain-boundary segregation. The model predicts that grain boundaries can be the primary storage sites for elements with large ionic radius--that is, incompatible elements in the Earth's mantle. This observation provides a mechanism for the selective extraction of these elements and gives a framework for interpreting geochemical signatures in mantle rocks.

Journal Article↗