SEARCH · Search PubMed
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.
Leaves of plants have the ability to accumulate the long-lived fission product (99)Tc. In the present work, an attempt was made to separate and characterize technetium species formed in maize grown on soil contaminated with Tc(VII)O(4)(-) solution. Data obtained from selective extraction, a Phosphorimager and liquid scintillation were employed.
The mechanism of poly ADPR synthesis and the transfer of poly ADPR to histone H1 molecule by electrophoretically homogenous calf thymus poly ADPR polymerase containing DNA was examined. 1) An acid insoluble radioactive complex (I) was obtained after incubation of purified enzyme with [3H] NAD. The stability of (I) was examined by SDS-polyacrylamide gel electrophoresis. The complex (I) was stable against acid, SDS, urea, DNase and RNase, but labile against pronase, trypsin, alkali and snake venom phosphodiesterase treatment. The molecular weight of (I) was about 130 000 daltons estimated by SDS-gel electrophoresis. The radioactive products of successive alkali, venom phosphodiesterase and Pronase hydrolysis of (I) were PR-AMP and AMP. The mean chain length of poly ADPR of (I) was 20--30. These results suggest that the complex (I) is poly ADP-ribosylated poly ADPR polymerase. 2) Besides (I), a second radioactive peak (II) was observed when acid insoluble products obtained from an incubation mixture containing purified poly ADPR polymerase, [3H] NAD and purified histone H1 were analyzed on SDS-polyacrylamide gel electrophoresis. The molecular weight of (II) was estimated to be about 23 000 daltons. The complex (II) is eluted like histone H1 on CM-cellulose columns and hydrolyzed by alkali, trypsin and snake venom phosphodiesterase but not by DNase, or RNase. The comples (II) was extracted selectively by 5 per cent perchloric acid or 5 per cent trichloroacetic acid from mixture of (I) and (II). The mean chain length of poly ADPR of complex (II) and 5--20; these results suggest that the complex (II) is poly ADP-ribosylated histone H1. 3) Results 1) and 2) indicate that purified DNA containing, thus DNA independent, poly ADPR polymerase catalyzes two different reactions, the ADPR transfer onto the enzyme itself and onto histone H1 and the elongation of ADPR chains. Dimeric forms of ADP-ribosylated histone H1 was not observed. Free poly ADPR was observed only when very small quantities of enzyme were used for incubation.
Context-dependent associative memories are models that allow the retrieval of different vectorial responses given a same vectorial stimulus, depending on the context presented to the memory. The contextualization is obtained by doing the Kronecker product between two vectorial entries to the associative memory: the key stimulus and the context. These memories are able to display a wide variety of behaviors that range from all the basic operations of the logical calculus (including fuzzy logics) to the selective extraction of features from complex vectorial patterns. In the present contribution, we show that a context-dependent memory matrix stores a large amount of possible virtual associative memories, that awaken in the presence of a context. We show how the vectorial context allows a memory matrix to be representable in terms of its singular-value decomposition. We describe a neural interpretation of the model in which the Kronecker product is performed on the same neurons that sustain the memory. We explored, with numerical experiments, the reliability of chains of contextualized associations. In some cases, random disconnection produces the emergence of oscillatory behaviors of the system. Our results show that associative chains retain their performances for relatively large dimensions. Finally, we analyze the properties of some modules of context-dependent autoassociative memories inserted in recursive nets: the perceptual autoorganization in the presence of ambiguous inputs (e.g. the disambiguation of the Necker's cube figure), the construction of intersection filters, and the feature extraction capabilities.
Water sorption by plant cuticular membrane isolates, mainly identified as polysaccharides, after selective extraction of the lipid components waxes and cutin was measured over the whole range of water activity. From water sorption isotherm, the strengths of water binding and water clustering were estimated. Data obtained by differential scanning calorimetry and Fourier-transform and near infrared spectroscopy confirmed the existence of water molecules in different macromolecular environments.
A high-performance liquid chromatographic method has been developed for the determination of metapramine in human plasma and urine. After selective extraction and derivatization with dansyl chloride, metapramine and the internal standard (maprotiline) are chromatographed on a reversed-phase LiChrosorb RP-18 column using a mixture of water--acetonitrile (35:65) as mobile phase. The eluted compounds are measured using a fluorescence detector. The detection limit of the assay for plasma and urine samples is about 1 ng/ml. The method has been successfully applied in a pharmacokinetic study following intravenous administration of 35 mg of metapramine.
A high-performance liquid chromatographic method has been developed for the determination of pipotiazine in human plasma and urine. After selective extraction, pipotiazine and the internal standard (7-methoxypipotiazine) and chromatographed on a column packed with Spherosil XOA 600 (5 micrometers) using a 7:3 (v/v) mixture of diisopropyl either--isooctane (1:1, v/v + 0.2% triethylamine and diisopropyl ether--methanol (1:1, v/v) + 0.2% triethylamine + 2.6% water. The eluted compounds are measured by fluorescence detection. The sensitivity of the method was established at 0.25 ng/ml pipotiazine in plasma and 2 ng/ml pipotiazine in urine (C.V. less than 5%). The method has been successfully applied to a pharmacokinetic study following a single oral administration of 10 mg of pipotiazine.
A high-performance liquid column chromatographic technique is reported for the analysis of some tryptophan and phenylalanine acid metabolites in the urine. An acidified and NaCl-saturated urine sample is loaded on to a C18-bonded silica microcolumn. After washing the microcolumn with clean and deionized water, the metabolites of interest are selectively extracted by successive elutions with organic solvents of variable polarity. Acids are eluted first and the neutral compounds with the next fraction. Basic compounds and other neutral substances of higher polarities were eliminated during the washing procedure. The chromatography was performed in the straight-phase isocratic elution mode utilizing 5-micrometers silica-gel columns loaded with a triethanolammonium perchlorate--perchloric acid aqueous solution. The separation achieved have permitted the application of the chromatographic technique to the analysis of urinary metabolites with acceptable accuracy.
A rapid, sensitive, and specific high-performance liquid chromatographic assay was developed for the determination of trimethoprim in blood, plasma, and urine using normalphase (adsorption) chromatography on a microparticulate silica column and UV monitoring at 280 nm. Trimethoprim is selectively extracted from the biological sample matrix at alkaline pH with chloroform, providng nearly quantitative extraction (greater than 95%) and a sensitivity limit of 0.01 to 0.02 microgram/ml blood or plasma, without interference from sulfonamides.
A method is described for the quantitation of flunarizine in biological fluids including plasma, urine, milk, fecal and tissue homogenates using the analogue cinnarizine as the internal standard. As little as 1.5 ng of flunarizine per ml of plasma can be accurately quantitated, this being achieved by the combination of a selective extraction procedure and a nitrogen detector. The method has been used to determine the concentration of flunarizine in biological fluids in support of human and animal pharmacokinetic studies.
Selective extraction of a 36-amino-acid peptide (DP-178, T20, pentafuside) from the protein matrices of animal and human plasma was achieved using acetonitrile containing 1% trifluoroacetic acid and 1% n-nonyl-beta-D-glucopyranoside. The peptide concentration of the extract was measured using reversed-phase high-performance liquid chromatography (RP-HPLC) and fluorescence detection. The eluent was excited at 280 nm and the intrinsic fluorescence signal was collected at 350 nm. Recovery of T20 from the plasma matrices was 75% (mouse), 60% (rat), 50% (cynomolgus monkey), and 55% (human) based on parallel-processed aqueous T20 standard solutions. The fluorescence peak area vs. concentration of T20 was linear in the range 4-160 ng/ml based on the final solute concentration in the HPLC vial, corresponding to original plasma concentrations of 100-4000 ng/ml. Experiments with truncated analogs of T20 demonstrate that this assay offers the advantage of detecting metabolites attributable to bio-transformation degradation processes differing by as little as one amino acid from the original peptide.
The successful introduction of a charged dextran into the Triton X-114 phase separation system for the selective extraction of cytochrome b5 (cyt. b5) in liver microsomes is described. In the absence of charged dextran, 55% of total microsomal proteins and 84% of cyt. b5 were extracted into the surfactant-rich phase. In the presence of anionic dextran sulfate, the extractability of total microsomal proteins was greatly reduced while that of cyt. b5 was increased. After triplicate extraction, cyt. b5 was purified more than 10-fold from microsomes with a recovery of 91% in the surfactant-rich phase. In view of its operational simplicity, this method provides a good means for the partial purification of cyt. b5 prior to chromatographic separations.
The analytical and biotechnological applications of human hemoglobin immobilized covalently on CNBr-Sepharose 4B are reviewed. Hemoglobin is bound to the matrix as alphabeta dimers via either chain. The immobilized alphabeta dimers maintain the capacity to interact reversibly with soluble ones under conditions where the soluble protein is in self-association equilibrium. Under these conditions, therefore, immobilized dimers bind part of the soluble protein. In turn, the binding process can be used to assess the specific features of the equilibrium on solid-phase and to extract selectively hemoglobin from a variety of biological specimens of practical interest. A different application of immobilized alphabeta dimers concerns their use in the determination of the equilibrium and kinetic stability of the heme-globin linkage, a property that is directly correlated with the stability of the hemoglobin molecule. The advantages and limitations attendant the use of the immobilized protein relative to the soluble one are discussed.
A novel, highly sensitive method for the determination of pilocarpic acid (PA) in human plasma is described. In addition, the method provides for the conversion of the lactone, pilocarpine (P), to PA so that a total drug presence can be determined. Using novel high-performance liquid chromatographic conditions capable of separating P, isopilocarpine (I-P), PA and isopilocarpic acid (I-PA) from each other and from endogenous plasma impurities, it was confirmed that P exclusively and quantitatively converts to PA in heparinized human plasma during storage. For the determination of PA, the selective extraction of PA from protein-free plasma was accomplished using two different solid-phase extraction (SPE) cartridges in two consecutive SPE steps. After extraction, PA was lactonized with trifluoroacetic acid back to P, and both P and an internal standard were acylated using heptafluorobutyric anhydride (HFBA). The trifluoroacetylated derivatives were monitored using gas chromatography (GC) with mass spectrometric (MS) detection. This procedure allowed the sensitive and reliable determination of PA with a limit of quantification (LOQ) of 1 ng/ml, which could not be achieved using previously described methods. The assay was validated in the concentration range of 1 to 10 ng/ml with an intra-day precision (expressed as the coefficient of variation, C.V.) ranging from 9.9 to 0.5%. Inter-day precision for the quality control standard at 2.5 ng/ml showed a C.V. of 10.2%. Accuracy ranged from 94 to 102%. The assay was used to monitor the maximum systemic exposure to P, administered by the ocular route, in terms of total plasma PA (P and PA).
A rapid, sensitive and enantioselective HPLC assay for the simultaneous determination of the reference 5-HT1A receptor agonists, R-(+)- and S-(-)-8-hydroxy-2-(di-n-propylamino)tetralin (R-8-OH-DPAT and S-8-OH-DPAT, respectively), in rat blood is presented. A selective extraction procedure was developed using a preliminary sample clean-up followed by isolation of R- or S-8-OH-DPAT on mixed-mode NARC-2 solid-phase columns. Separation of the enantiomers was performed by high-performance liquid chromatography using a Chiracel OD-R column. Detection was obtained using an electrochemical detector set at a voltage of 0.63 V. The mobile phase consisted of a 50 mM phosphate buffer (pH 5.5)-acetonitrile (80:20, v/v) mixture. At a flow-rate of 1 ml min(-1), the total run time was approximately 14 min. The limit of detection for R- and S-8-OH-DPAT was 0.5 ng ml(-1). In the concentration range between 50 ng ml(-1) and 1000 ng ml(-1) intra- and inter-day relative standard deviations were less than 12%. The assay was applied to a pharmacokinetic-pharmacodynamic study in rats in which decrease of body temperature was used as a measure of 5-HT1A receptor-mediated effect. Values for clearance, volume of distribution at steady state and terminal elimination rate constant were 22+/-2 ml min(-1), 1969+/-473 ml and 156+/-34 min for R-8-OH-DPAT and 16+/-1 ml min(-1), 3353+/-347 ml and 334+/-36 min for S-8-OH-DPAT, respectively. No enantiomeric interconversion was observed in vivo from R-8-OH-DPAT to S-8-OH-DPAT or vice versa.
Equilibrium properties and kinetics of metoclopramide release of carbomer-metoclopramide (C-M) hydrogels are reported. A set of (C-M)(X) (x=moles percent of M=50, 75, 100) that covers a pH range between 6.49 and 8.40 was used. Hydrogels exhibited a high negative electrokinetic potential (zeta). Concentrations of ion pair [R-COO(-)MH(+)] and free species [M] and [MH(+)] were determined by the selective extraction of M with 1,2-dichloroethane (DCE) together with pH measurements. The system (C-M) is characterized by a high proportion of drug present in the form of ion pairs and a negative zeta potential that attracts MH(+) and H(+) and repeals OH(-), providing a microenvironment of higher acidity than the bulk medium. Delivery rates of M were measured in a Franz type bi-compartmental device using water and NaCl 0.9% solution as receptor media. (C-M) hydrogels behave as a reservoir that releases the drug at a slow rate to water; the rate increases 14 times as water is replaced by NaCl solution. The pH effect on delivery rate suggests that, under the main conditions assayed, the rate of dissociation of R-COO(-)MH(+) together with the low change of pH in the polyelectrolyte environment are the factors that control releasing rates.
This is a case report of a 23-year-old black woman with a skeletal Class II Division 1 malocclusion and an anterior open bite. The maxillary central incisor root was severely dilacerated, a maxillary lateral incisor and canine were transposed, a maxillary canine was impacted near the orbital rim, and a mandibular second premolar was congenitally missing. Selective extractions and attention to detail provided outstanding occlusal function and improved facial esthetics.
By using sodium dodecyl sulfate-polyacrylamide gel electrophoresis and immunoblotting assays in the presence of polyclonal antiserum raised against electrophoretically specific polypeptides of colorectal cancer nuclear polypeptides with M(r) of 35-40 kDa, we have identified p36 protein whose expression accompanies tumorigenesis of large intestine. Immunological analysis of 35 nuclear protein preparations has indicated expression of p36 antigen in nine of 11 right-sided (81.8%) and 21 of 24 (87.5%) left-sided colorectal tumor cases, but not in any control tissue samples. In this study, we have identified p36 antigen in two colon tumor cell lines, i.e., SW620 and HT29 as well. Fractionation experiments based on selective extraction of nuclei isolated from cancerous specimens, which enables their separation into chromatin, nuclear matrix and its subfraction, i.e., internal and peripheral matrix have revealed the concentration of this particular antigen in the internal matrix.
Under physiological conditions, small amounts of free arachidonic acid (AA) are released from membrane phospholipids, and cyclooxygenase (COX) and acyl-CoA synthetase (ACS) competitively act on this fatty acid to form prostaglandins (PGs) and arachidonoyl-CoA (AA-CoA). To clarify factors deciding the metabolic fate of free AA into these two pathways, we investigated the effects of a nitric oxide (NO) donor 1-hydroxyl-2-oxo-3-(N-methyl-3-aminopropyl)-3-methyl-1-triazene (NOC7), and peroxynitrite (ONOO(-)) on the formation of PG and AA-CoA from high and low concentrations of AA (60 and 5 micro M) in rabbit kidney medulla microsomes. The kidney medulla microsomes were incubated with 60 or 5 micro M [14C]-AA in 0.1M Tris/HCl buffer (pH 8.0) containing cofactors of COX (reduced GSH and hydroquinone) and cofactors of ACS (ATP, MgCl(2) and CoA). After incubation, PG (as total PGs) and AA-CoA were separated by selective extraction using petroleum ether and ethyl acetate. When 60 micro M AA was used as the substrate concentration, NOC7 stimulated the PG formation at 0.5 micro M, and inhibited it at 50 and 100 micro M, without affecting the AA-CoA formation. When 5 micro M AA was used as the substrate concentration, NOC7 showed no effect on the PG and AA-CoA formation up to 10 micro M or below, but enhanced the AA-CoA formation with a coincident decrease in the PG formation at 50 micro M or over. Experiments utilizing a NO antidote, carboxy-2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl 3-oxide, revealed that the observed effects of NOC7 using 60 and 5 micro M AA are caused by NO. On the other hand, ONOO(-) stimulated the PG formation from 60 micro M AA, with no alteration in the AA-CoA formation at a concentration of 100 micro M, but when 5 micro M AA was used as the substrate concentration, it was without effect on the PG and AA-CoA formation. These findings indicate that actions of NO and ONOO(-) on the PG and AA-CoA formation by the kidney medulla microsomes may change depending on the substrate concentration. The effects of NO using 5 micro M AA were reversed by the addition of the superoxide generating system (xanthine-xanthine oxidase plus catalase), indicating that superoxide is a vital modulator of the action of NO. These results suggest that NO, but not ONOO(-), can be a regulator of the PG and AA-CoA formation at low substrate concentrations (close to the physiological concentration of AA), and that superoxide may play an important role in the action of NO.