Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Separation”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,315 records · Page 73Linked to original sources
PubMed1993

Size-dependent separation of proteoglycans by electrophoresis in gels of pure agarose.

An improved system for electrophoresis of proteoglycans is presented, using a discontinuous buffer system that allows stacking of the sample. The molecular sieving in pure agarose was studied using cartilage proteoglycans separated into fractions of different size (Kav value) by gel chromatography. These fractions were used to establish the relationship between size and mobility in agarose gels of different concentrations. With low agarose concentration, the separation was largely dependent on charge density. With increasing agarose concentration, the separation became increasingly dependent on size. Electrophoresis provides a suitably sensitive tool for analysis of the proteoglycan and glycosaminoglycan fractions prepared by the Alcian blue precipitation described in the preceding paper. Alcian blue precipitated cartilage proteoglycans appeared identical in size to molecules prepared by conventional procedures when analyzed by electrophoresis. Proteoglycans of various sizes were prepared by precipitation with Alcian blue of 4 M guanidine-HCl extracts of bovine nasal cartilage, human articular cartilage, human skin, and bovine sclera. Proteoglycans were also precipitated from human synovial fluid and plasma. The samples were electrophoresed on 1.2% agarose gels, which was the highest agarose concentration suitable for large aggregating proteoglycans but still separating the smallest proteoglycans with one or two glycosaminoglycan chains from each other. Several sizes of proteoglycans were found in each sample except blood plasma, which only contained one small proteoglycan/glycosaminoglycan. Electrophoresis in agarose is also suitable for separating proteoglycan aggregates and monomers and allows rapid analysis of several samples at a time. The proteoglycans prepared by Alcian blue precipitation retained their ability to form aggregates with hyaluronic acid.(ABSTRACT TRUNCATED AT 250 WORDS)

Alcian Blue↗
PubMed1993

Separation and quantitation of monoclonal antibody aggregates by asymmetrical flow field-flow fractionation and comparison to gel permeation chromatography.

During the downstream processing of monoclonal antibodies (Mab) the formation of dimers and/or oligomers may occur. Today, the most common technique for determination of aggregate content is gel permeation chromatography (GPC) but it has limited resolution and separation speed. Oligomers are particularly difficult to resolve. Asymmetrical flow field-flow fractionation (FFF) is a new analytical method for the separation of Mab aggregates. The monomer and dimer peaks were well resolved and three additional peaks, thought to be trimers, tetramers, and pentamers were partially resolved. The total time for a separation can be kept as short as 6 min. The GPC separation takes about 15 min with less resolution. A study of the reproducibility for the two techniques revealed that the precision was slightly better for GPC. Investigation of the dependence of sample concentration showed that the load limit for FFF was about 4 micrograms of Mab. The GPC technique requires prefiltered samples in order to avoid clogging of the column. For FFF it is possible to inject samples containing precipitated material without any pretreatment. The flow conditions can be adjusted so that the precipitated material elutes with the front, well separated from the monomer peak.

Antibodies, Monoclonal↗
PubMed1994

Chiral separation by capillary affinity zone electrophoresis using an albumin-containing support electrolyte.

Chiral separations of some pharmaceutical compounds were studied by capillary affinity zone electrophoresis. Bovine serum albumin (BSA) was used as a chiral selector and added to electrolyte. For the chiral separation of new quinolone bactericidal reagents, phosphate buffer was more appropriate than borate buffer solution as the support electrolyte. The effects of BSA concentration, albumin type, pH, chiral additive, and voltage on separation were observed. As a result, chiral separations were performed in the pH range 7-8. The migration and stereoselectivities of enantiomers were changed by varying the protein concentration (more than 0.2% w/v) and voltage and by adding amino acids as chiral modifiers. This procedure is easily applicable to other compounds for chiral separation or for studies of protein binding interaction.

Anti-Infective Agents↗
PubMed1995

Methods for separation of free, short, medium, and long chain fatty acids and for their decarboxylation.

A system for separation and quantitation of free fatty acids by HPLC is described. This system provides for separation of short, medium, and long chain, saturated from unsaturated, branched from unbranched free fatty acids, and iso- from anteiso-branched acids of equal carbon number, and for their quantitation. An efficient method and inexpensive apparatus for performing the Schmidt degradation on separated acids is also presented. Standard and plant-derived branched and straight chain fatty acids were investigated using these methods. The latter were radiolabeled in vivo and released from trichome-exudated sugar esters by saponification. Free fatty acids were separated by reversed-phase C-18 HPLC using gradients of acetonitrile/H2O, containing 0.01 M H3PO4. Separated acids were converted to their potassium salts and transferred to easily and inexpensively fashioned, triple-well septum vials containing a center well for trapping CO2. Sulfuric acid was placed in a tip well atop the center well and the vial was closed. Tipping the vial allowed the acid to spill to the sample without the need to puncture the septum or transfer acid via a syringe. The system allowed for the introduction of an additional CO2-trapping reagent, midreaction. This arrangement improved CO2 recovery to 99-100% and its reproducibility to about +/- 3%.

Acetonitriles↗
PubMed1996

Sequence-dependent DNA separation by anion-exchange high-performance liquid chromatography.

High-performance liquid chromatography (HPLC) system with a new nonporous anion-exchange resin, DNA-NPR, made it possible to rapidly separate DNA fragments up to 20 kbp with high resolution. In order to further characterize this chromatographic DNA separation system, we prepared a mixture of double-stranded DNAs of constant length carrying a fully degenerated 50-bp region and analyzed their chromatographic behavior on the DNA-NPR column. The results indicated that the separation of DNA fragments on the anion-exchange HPLC was governed not only by size, but also by nucleotide sequence: even DNA fragments with the same size and the same base content could be separated on this column. Taking advantage of this characteristic feature of the anion-exchange HPLC, we could readily fractionate human cDNAs with practically acceptable recovery and high resolution. Furthermore, the combination of HPLC and gel electrophoresis realized separation of a mixture of DNA fragments in a two-dimensional pattern.

Base Sequence↗
PubMed1997

Comparison between HPLC and capillary electrophoresis for the separation and identification of the platination products of oligonucleotides with cis-[Pt(NH3)2(H2O)2]2+ and [Pt(NH3)3(H2O)]2+.

HPLC and capillary electrophoresis (CE) were compared in order to separate the platinum adducts formed upon reaction of the double-stranded 18-mer d(AACGGTTAACCGTTAATT)2 I with the two complexes cis-[Pt(NH3)2(H2O)2]2+ 1 and [Pt(NH3)3(H2O)]2+ 2 and of the single-stranded octamer d(CTGGCTCA) II with complex 2. The GG sequence in both oligonucleotides is the only site of platination giving monoadducts on either of the two guanines or the diadduct which is the N7,N7 chelate of the Pt(NH3)(2+)2 moiety. The HPLC separation of the adducts was performed with a reverse-phase technique similar to that previously used for platinated oligonucleotides up to octamers. The adducts were identified by enzymatic digestion followed by mass spectrometry characterization of the digests collected at the outlet of the column. The CE separation of the platination products of I with 2 and 1 was performed using respectively a simple capillary zone electrophoresis technique and a micellar electrokinetic capillary chromatography technique. For the more difficult separation of the platination products of II with 2, a capillary gel electrophoresis techniques was required. In contrast to HPLC, CE gives better resolution the longer the oligonucleotide. Moreover, the separations are run with higher efficiency and time saving. However, with the present machines, CE precludes the recovery of sufficient amounts of material required by product identification.

Chromatography, High Pressure Liquid↗
PubMed2001

Fluorescence immunoassay system based on the use of a pH-sensitive phase-separating polymer.

Poly(N-isopropylacrylamide-co-methacrylic acid) [P(NIPAAm-co-MAA)], a linear water-soluble pH-sensitive phase-separating polymer, was synthesized and used as a novel separation carrier for the reactants in immunoassay. This polymer precipitates out of water below a critical pH 5.8 at 37 degrees C and redissolves when the pH of solution is above 6.2. The characteristic of this polymer makes it possible to carry out the immunochemical steps of an immunoassay in a true solution and then to quickly separate the resulting product from the reaction mixture. The above approach was applied to determination of alpha-fetoprotein with the competitive immunoassay format. Compared with traditional ELISA using the same reactants, the proposed method was much faster (the assay time decreased from 100-120 to 30 min) and showed similar sensitivity, i.e., 0.04 ng/mL. In addition, a sandwich immunoassay method for the determination of hepatitis B surface antigen was also studied, and the results showed that the pH phase-separating immunoassay could be carried out through a sandwich or a competitive method. This general technique may also be used for a wide variety of separation processes in addition to immunoassay, in which a specific component is to be isolated for analysis, recovery, or disposal.

Acrylamides↗
PubMed2000

Development and control of tissue separation at gastrulation in Xenopus.

During Xenopus gastrulation, the internalizing mesendodermal cell mass is brought into contact with the multilayered blastocoel roof. The two tissues do not fuse, but remain separated by the cleft of Brachet. This maintenance of a stable interface is a precondition for the movement of the two tissues past each other. We show that separation behavior, i.e., the property of internalized cells to remain on the surface of the blastocoel roof substratum, spreads before and during gastrulation from the vegetal endoderm into the anterior and eventually the posterior mesoderm, roughly in parallel to internalization movement. Correspondingly, the blastocoel roof develops differential repulsion behavior, i.e., the ability to specifically repell cells showing separation behavior. From the effects of overexpressing wild-type or dominant negative XB/U or EP/C cadherins we conclude that separation behavior may require modulation of cadherin function. Further, we show that the paired-class homeodomain transcription factors Mix.1 and gsc are involved in the control of separation behavior in the anterior mesoderm. We present evidence that in this function, Mix.1 and gsc may cooperate to repress transcription.

Activins↗
PubMed1997

Towards a molecular understanding of phase separation in the lens: a comparison of the X-ray structures of two high Tc gamma-crystallins, gammaE and gammaF, with two low Tc gamma-crystallins, gammaB and gammaD.

gamma-Crystallins, although closely related in sequence, show intriguing differences in their temperature-dependent interactions: those that have a high or intermediate Tc for phase separation are cryoproteins whereas low Tc gamma-crystallins are not. To address the molecular basis of phase separation, X-ray crystallography has been used to define the structural differences between high and low Tc gamma-crystallins. A pre-requisite for this study was to clarify the assignment of bovine gene sequences to bovine gamma-crystallin proteins used for biophysical measurements. Based on nucleotide sequence analyses of gamma E and gamma F bovine crystallin genes, gamma F corresponds to the previously crystallised high Tc protein bovine gamma IVa and gamma E corresponds to the high Tc bovine protein fraction previously known as gamma IIIa. The gamma F sequence has enabled the completion of the refinement of the bovine gamma F crystal structure which shows that the molecule has an additional surface tryptophan explaining why gamma F has different spectroscopic properties from gamma B. A high Tc protein from rat lens, gamma E crystallin, has been crystallised and the X-ray structure solved at 2.3 A resolution. Comparison of the X-ray structures of two high Tc proteins, rat gamma E and bovine gamma F, with the structures of two low Tc proteins, bovine gamma B and bovine gamma D, shows that the main conformational change between high and low Tc proteins is in the cd surface loop of motif 3. All four structures have numerous ion pairs on their surfaces leading to a high surface charge density, yet with low overall charge. Comparison of the lattice contacts of the two high Tc proteins with the two low Tc gamma-crystallins indicates that these high Tc proteins utilise more amino-aromatic interactions such as between histidine and arginine. Comparison of the sequences of all the gamma-crystallins which have been characterised for phase separation temperature indicates that only residue Arg/Lys 163 uniquely distinguishes cryo from non-cryo gamma-crystallins and it is close to the altered surface loop. Although this region probably contributes to phase separation, Tc is likely to be a function of an overall global property that is responsive to overall charge distribution. Calculated dipole moments of native gamma-crystallins, low Tc gamma-crystallin sequences threaded into high Tc gamma-crystallin structures, and vice versa, show how both sequence and 3D structure contribute to this overall property. High Tc gamma-crystallins have on average higher Arg/Lys ratios and higher histidine content. It is hypothesised that this increases the proportion of surface static paired charged networks which thus reduces the repulsive hydration force and so increases the attractive interactions of the protein-rich phase in binary liquid phase separation.

Amino Acid Sequence↗
PubMed1997

Effect of the Form of the Quaternary Ammonium Ion on the Ion-Pair Phase Separation Phenomenon with Perfluorooctanoic Acid

The effect of the form of 10 types of quaternary ammonium ions (Q+) for the phase separation phenomenon, which accompanies a charge neutralization with perfluorooctanoate ion (PFOA-) and Q+, was studied. The separated phase using the spherical form of Q+ (i.e., [4·4·4·4], [3·3·5·5], [3·3·3·7], and [2·2·6·6], where the numbers in square brackets represent the carbon numbers of four kinds of straight alkyl chains which were directly bonded to the nitrogen atom) was in the liquid state. On the other hand, the separated phase using the rod form ([2·2·2·10] and [1·1·1·13]) was in the solid state. The volume, specific gravity, and water content of the liquid-separated phase using [3·3·5·5] were 116 &mgr;l, 1.27, and 6.98%, respectively, under the following experimental conditions: [Q+]T = 2.30 x 10(-2) mol dm-3, [PFOA-]T = 5.75 x 10(-3) mol dm-3, and 25°C. This liquid phase was stable to physical changes such as Q+ total concentration and temperature, compared with three other types of Q+ ([4·4·4·4], [3·3·3·7], and [2·2·6·6]), which formed similar liquid-separated phases.

Journal Article↗
PubMed2001

"Vector Chromatography": Modeling Micropatterned Separation Devices.

A repetitive sequence of quiescent fluid layers of differing viscosities through which small spherical Brownian particles move is analyzed in order to illustrate in a simple context how the theory of macrotransport processes, a generalization of Taylor dispersion theory, may be employed to rigorously analyze spatially periodic micropatterned chromatographic separation devices for circumstances in which the solute species to be separated are animated by the action of species-specific external forces oriented asymmetrically relative to the body-fixed pattern. In the generic "vector" separation scheme, illustrated by our elementary example, the different species undergoing separation move, on average, in different directions relative to pattern-fixed axes, whence their chromatographic sorting is effected according to their different mean angular trajectories through the device. This scheme differs fundamentally from traditional "scalar" chromatographic separation schemes, wherein all species move on average parallel to the animating force (including circumstances in which they are passively entrained in a unidirectional solvent flow) and hence for which the sorting is effected by the relative speeds of the several species through the chromatographic column. Vector chromatography is quantified by two global "macrotransport coefficients", namely the solute mobility dyadic M* (representing the tensor proportionality coefficient between the mean solute velocity vector U* and the external force vector F acting upon the solute molecules) and the dispersivity dyadic D* (resulting from the deviation of the instantaneous position of the particle from its mean position based upon its mean velocity vector). In the present example these coefficients are studied parametrically as functions of: (i) the orientation of the external force relative to the symmetry axis of the fluid layers; (ii) the local viscosity distribution within a layer; (iii) the vector particle Peclet number (constructed from the vector force, the length of the viscosity period, and the Boltzmann factor kT); and (iv) the thermodynamic interphase solute partition distribution coefficient between the two fluid layers comprising a unit cell. Copyright 2001 Academic Press.

Journal Article↗
PubMed2000

Changes in the 17 bp spacer in the P(R) promoter of bacteriophage lambda affect steps in open complex formation that precede DNA strand separation.

Tau plots and temperature-shift experiments were used to determine which step in the formation of transcriptionally-competent open complexes is affected by changing the length of the 17 bp spacer separating the -10 and -35 consensus regions of the P(R) promoter of bacteriophage lambda. Abortive initiation assays at 37 degrees C indicate that the primary effect of insertion of a base-pair, thereby increasing spacer length to 18 bp, is a decrease in k(f), the rate constant for conversion from closed (RP(c)) to open (RP(o)) complexes, by approximately a factor of 4. The mutation did not significantly affect K(B), the equilibrium constant for formation of closed complexes, and decreased K(B)k(f) by a factor of 3. Deletion of a bp to create a 16 bp spacer had a much greater effect, decreasing the measured value of k(f) by a factor of about 25 to 30, and K(B)k(f) by a factor of 7 to 8. When the values of the parameters for the deletion mutant were corrected for incomplete occupancy of RP(o) at equilibrium, the effects of the deletion were even greater. In particular, the corrected value of K(B)k(f) was about 15 times lower than the corresponding value for two promoters with wild-type spacing. Based on temperature shift experiments, the changes in spacer length did not affect the equilibrium at 20 degrees C between RP(i), a stable intermediate in which DNA strands are not separated, and RP(o). Although differential sensitivity of single-stranded bases to KMnO(4) indicated that in about 20% of the open complexes at 20 degrees C the DNA strands are not fully separated (RP(o1)), the distribution between these complexes and RP(o2) (DNA strands fully separated) was also not affected significantly by changes in spacer length. Thus, changes in spacer length primarily affect k(2), the rate constant for conversion of RP(c) to RP(i), which corresponds to a nucleation of DNA strand-separation. Application of published data and/or algorithms for determining effects of nucleotide sequence on twist angle or rise at individual bp steps does not provide a simple explanation of the difference in promoter strength between P(R) derivatives with 16 bp spacing and those with 18 bp spacing.

Algorithms↗
PubMed1990

Separation of neural and surface ectoderm after closure of the rostral neuropore.

Separation of neural and surface ectoderm after closure of the rostral neuropore in the head region has been described by investigating the integrity of the basement membranes of these epithelia in 11- to 27-somite rat embryos. The basement membranes were visualized with polyclonal antibodies against laminin. Furthermore, cell degeneration has been investigated in relation to neural crest activity, and discontinuities of the basement membrane in 9- to 30-somite mouse embryos. The separation of the basement membranes of neural and surface ectoderm in the midline is a final phase during the fusion of the neural folds, which takes place from the closure of the rostral neuropore, at the 19-somite stage, until the 27-somite stage (rat embryos), and which occurs focally with variation in the midsagittal and the transverse planes. In the prosencephalon, neural crest activity is absent during the separation phase of both epithelia, but cell degeneration may contribute to the separation of the initially connected basement membranes. A disturbance in the separation of the neural and surface ectoderm may be the pathogenetic basis of midline skull defects, and of the fronto-ethmoidal encephalocele in particular.

Animals↗
PubMed1980

The effect of cyclophosphamide and isoniazid (INH) alone and in combination on the centromere separation sequence in Chinese hamster bone marrow cells.

X-irradiation of Chinese hamsters with 50 and 200 rad delayed the centromere separation of bone marrow chromosomes. Combination of a treatment with 13.3 mg cyclophosphosphamide/kg body wt. and 50 rad did not result in an enhanced effect compared with the single treatments. Again, the separation sequence was not influenced. No delay was induced by a treatment with 125 mg isoniazid/kg, but a slightly and significantly earlier separation of the chromatids in both groups of metacentric and acrocentric chromosomes occurred. The separation delay seen after irradiation with 50 rad disappeared when the animals were pretreated with isoniazid. Independently of these results the asynchronous separation sequence was not altered in any of the experiments.

Animals↗
PubMed1988

Parental centromere separation sequence and aneuploidy in the offspring.

We have studied the centromere separation sequence in lymphocyte mitoses of the parents of four infants with trisomy 18, five patients with trisomy 21, and five children with normal karyotype. "Late separation" of chromosome 18 was found in both parents of a neonate with trisomy 18, "early separation" of chromosome 21 in three mothers and in one father of four children with trisomy 21. No "out-of-phase" separation occurred in the mitoses of the parents of normal children. The findings provide further evidence for the correlation between alteration of the parental centromere separation sequence and aneuploidy of the offspring.

Aneuploidy↗
PubMed1980

Further consideration on pattern separability in a random neural net with inhibitory connections.

A two-layer random neural net with inhibitory connections composing of threshold elements has been regarded as a model of the cerebellar cortex. Many properties of pattern separation with the model have been disclosed through consideration on the degree of pattern separation. However, we have not shown yet that the degree of pattern separation is given by some different functions which are decided by the relation between the firing rates of input patterns. The present study is intended to reveal that the functions of the degree of pattern separation are synthesized with some different partial functions, and they are differently given on the relation between the firing rates of input patterns. Simultaneously, it is proved that the number of the functions also depend on the number of connections between two layers in the model. We also disclose the properties of the degree of pattern separation, and give some suggestions on the sizes of the firing rates of mossy fibers and granule cells under the knowledge about them.

Cerebellar Cortex↗
PubMed1993

Abuse of codeine separated from over-the-counter drugs containing acetylsalicylic acid and codeine.

In Denmark a new trend concerning the abuse of codeine has been observed. Danish drug abusers have discovered that codeine is easily separated from certain drugs containing acetylsalicylic acid and codeine. When separated the codeine can be used either orally or intravenously. Three different drugs combining acetylsalicylic acid and codeine are available in Denmark, but codeine is only easily separable from one of these. Applying the same procedure to the two other drugs produces unpredictable or unfavourable ratios of codeine to acetylsalicylic acid. In several countries, however, similar drugs combining acetylsalicylic acid and codeine are available. It is not possible from a list of constituents to predict how easily codeine can be separated from a particular drug. Therefore it is strongly recommended that relevant drugs are tested at local forensic laboratories. In case codeine is found to be very easily separated from a product appropriate action should be taken.

Aspirin↗
PubMed1991

CSF monoamine metabolite concentrations vary according to age, rearing, and sex, and are influenced by the stressor of social separation in rhesus monkeys.

In humans, CSF monoamine metabolite concentrations have been shown to vary as a complex function of age, sex, psychiatric diagnosis, and stress. To test for such relationships in rhesus monkeys, 28 subjects, reared either in anxiety producing peer-only groups or in mother-infant dyads, were studied at 6, 18 or 50 months of age. Each monkey underwent a series of four 4-day social separations, each followed by 3 days of reunion. Prior to and during the first and fourth separations, CSF was obtained from the cisterna magna and assayed for the serotonin metabolite 5-HIAA, the dopamine metabolite HVA, and the norepinephrine metabolite MHPG. CSF 5-HIAA showed an age-related decline which was greater in the mother-reared subjects. Peer-only-reared males had an increased 5-HIAA concentration relative to females, and higher 5-HIAA levels than mother-reared males. MHPG was also higher in peer-only-reared monkeys than in mother-reared subjects at all ages. In both groups HVA declined across the three ages, and MHPG increased from the 18- to the 50-month measurements. Both MHPG and 5-HIAA concentrations increased during the initial social separation, although only MHPG remained elevated across the repeated separations; HVA, on the other hand declined during social separation. These results are discussed in terms of established anxiety and aggression differences between peer-only and mother-reared monkeys.

Aging↗