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At least 1,171 records · Page 65Linked to original sources
PubMed1995

Fumonisin B1 analysis with capillary electrophoresis-electrospray ionization mass spectrometry.

Fumonisin B1, a mycotoxin produced by a common fungal contaminant of corn, Fusarium moniliforme, was analyzed by capillary electrophoresis-electrospray ionization mass spectrometry. System performance was maximal with uncoated columns. System efficiencies of approximately 44,000 plates/m and reproducible analysis times of about 13 min were obtained. System efficiency with methyl-coated columns was approximately 24,000 plates/m. Reproducible analysis times of about 3.5 min were obtained with these columns. With uncoated columns, the concentration limit of detection was 156 ppb with a s/n ratio of approximately 10. The estimated injected mass at 156 ppb was 1.1 pg. Repeated injections of extracts containing constant fumonisin B1 concentrations showed that peak areas were slightly inconsistent, although generally similar to variations encountered with liquid chromatography-electrospray ionization mass spectrometry. The source of this inconsistency was traced to sample solubility, errors inherent in electrophoresis injections, and electrospray instability. Minimizing these problem areas will produce a technique with peak area reproducibilities comparable to liquid chromatography-electrospray ionization mass spectrometry, but with potentially greater resolving power.

Carcinogens, Environmental↗
PubMed1995

Sensitive detection and structural characterization of trimethyl(p-aminophenyl)-ammonium-derivatized oligosaccharides by electrospray ionization-mass spectrometry and tandem mass spectrometry.

Mass spectrometric methodologies which use electrospray ionization (ESI) for oligosaccharide structural determination and which are linked to classical procedures, such as reductive amination, have been established. Several derivatives of a model oligosaccharide were prepared and their ionization efficiencies in electrospray ionization (ESI) and fast-atom bombardment (FAB) mass spectrometry were investigated. The trimethyl-(p-aminophenyl)ammonium (TMAPA) derivatives showed extremely high sensitivity in positive-ion ESI-MS and gave Y- and Z-series sequence ions by ESI tandem mass spectromety (MS/MS). This study suggests that TMAPA-derivatized oligosaccharides used in ESI-MS and ESI-MS/MS would be effective for structural characterization of oligosaccharides that are available only in limited quantities.

Aminopyridines↗
PubMed2004

Selective determination of organophosphate flame retardants and plasticizers in indoor air by gas chromatography, positive-ion chemical ionization and collision-induced dissociation mass spectrometry.

Gas chromatography/ion trap mass spectrometry with in-source ionization and dissociation was used in positive-ion chemical ionization (PICI) mode for the determination of organophosphate triesters in indoor air. These compounds are widely used as additive flame retardants and plasticizers in different types of materials and have become ubiquitous pollutants in indoor environments. When using collision-induced dissociation in PICI mode the fragmentation of the organophosphate triesters can be performed in a more controllable way than in electron ionization (EI) mode. The developed selected-reaction monitoring method provided high selectivity for the investigated compounds. For 8-h air measurements (corresponding to 1.5 m3 of sampled air) the limit of detection of the method was determined to be in the range 0.1-1.4 ng m(-3), which is comparable with nitrogen-phosphorus detection and about 50-fold lower than when using EI in selected-ion monitoring mode. The presented method was applied to samples from three common indoor environments, in which a number of organophosphate triesters were identified and quantified. The dominating compound was found to be tris(2-chloropropyl) phosphate, which occurred at levels up to 0.8 microg m(-3).

Journal Article↗
PubMed2005

Impact of ionizing radiation on the life cycle of Saccharomyces cerevisiae Ty1 retrotransposon.

Ty1 elements, LTR-retrotransposons of Saccharomyces cerevisiae, are known to be activated by genetic and environmental stress. Several DNA-damaging agents have been shown to increase both Ty1 transcription and retrotransposition. To explore further the relationship between Ty1 mobility and DNA damage, we have studied the impact of ionizing radiation at different steps of the Ty1 life cycle. We have shown that Ty1 transposition is strongly activated by gamma-irradiation and we have analysed its effect on Ty1 transcription, TyA1 protein and Ty1 cDNA levels. The activation of transposition rises with increasing doses of gamma-rays and is stronger for Ty1 elements than for the related Ty2 elements. Ty1 RNA levels are markedly elevated upon irradiation; however, no significant increase of TyA1 protein was detected as measured by TYA1-lacZ fusions and by Western blot. A moderate increase in Ty1 cDNA levels was also observed, indicating that ionizing radiation can induce the synthesis of Ty1 cDNA. In diploid cells and ste12 mutants, where both Ty1 transcription and transposition are repressed, gamma-irradiation is able to activate Ty1 transposition and increases Ty1 RNA levels. These results suggest the existence of a specific regulatory pathway involved in Ty1 response to the gamma-irradiation that would be independent of Ste12 and mating-type factors. Our findings also indicate that ionizing radiation acts on several steps of the Ty1 life cycle.

Blotting, Northern↗
PubMed1995

Quantitative lipoxygenase product profiling by gas chromatography negative-ion chemical ionization mass spectrometry.

An assay for the quantitative determination of the hydroxylation profile of long-chain fatty acids is described for gas chromatography negative-ion chemical ionization mass spectrometry and stable isotope dilution using [carboxyl-18O2]-labeled internal standards. The assay has been applied to the study of fatty acids isolated from body fluids, tissue, and cultured cells. Examples for the analyses of biological systems expressing 5-, 8-, 12-, or 15-lipoxygenase activity are given and the most important sources of analytical errors are addressed. Increased specificity compared to analysis by negative-ion chemical ionization, at the cost of sensitivity, can be achieved by the use of positive-ion electron impact ionization for the investigation of hydrogenated pentafluorobenzylester/trimethylsilylether derivatives. The method described provides complete, specific, and quantitative profiles of hydroxylated fatty acids originally present in biological samples or generated in vitro by incubation with polyunsaturated fatty acid substrates such as linoleic or arachidonic acid.

Animals↗
PubMed1995

Electrospray-ionization mass spectrometry of molecular variants of a [2Fe-2S] ferredoxin.

The [2Fe-2S] ferredoxin from Clostridium pasteurianum is a homodimeric protein of which each subunit contains one [2Fe-2S] cluster. In previous investigations, the five cysteine residues in positions 11, 14, 24, 56 and 60 had been mutated into serine or alanine. The wild type ferredoxin and several of its molecular variants have now been analyzed by electrospray-ionization mass spectrometry. In the negative-ion detection mode, depending on the infusion solvent used, molecular peaks attributable to the apoprotein, to the monomeric holoprotein, and to the dimeric holoprotein were detected in all cases. The data confirmed the presence of the expected mutations, showed that all of these proteins contain one [2Fe-2S] cluster per subunit, and indicated that the dimeric structure of these ferredoxins could be retained in the conditions of the electrospray ionization. This investigation establishes the power of electrospray-ionization mass spectrometry for the analysis of oligomeric proteins containing labile metal clusters.

Alanine↗
PubMed1993

Distribution of hydrophobic ionizable xenobiotics between water and lipid membranes: pentachlorophenol and pentachlorophenate. A comparison with octanol-water partition.

We have studied distribution of pentachlorophenol (PCP)--a major environmental pollutant--between egg-phosphatidylcholine (egg-PC) membranes and water. The objectives were (1) to compare the membrane-water partition of the un-ionized (HA) and ionized (A) PCP, and (2) to establish similarities and differences between the partition of PCP into lipid membranes and into octanol. The studies were made with egg-PC liposomes. It is shown that the distribution isotherms can be understood in terms of the Langmuir-Stern-Grahame adsorption model. The model is applicable to both the HA and A species; it takes into account the electrostatic interactions at the membrane-water interface charged by the adsorbed pentachlorophenate. Relationships between the membrane surface adsorption and bulk partition characteristics were presented and used to relate the partition of PCP into egg-PC membranes to those for octanol-water systems. Results (egg-PC membranes): bulk distribution coeff. gamma HA = 2.9 x 10(5), gamma A = 1.6 x 10(4), association constant KmHA = 2.9 x 10(5) M-1, KmA = 0.7 x 10(5) M-1, adsorption site area PsHA = 0.6 nm2, PsA = 3.5 nm2, and linear partition coeff. Beta mHA = 550 microns, beta mA = 30 microns. Comparable to gamma HA and gamma A for octanol-water are P(ow)(HA) approximately 1.3 x 10(5) and P(ow)(A) approximately 30. The major difference is in the distribution of ionized PCP which is several hundred times greater for egg-PC membranes compared to octanol. The difference is associated with the properties of the membrane-water interface.

Membranes, Artificial↗
PubMed1980

Continuous in vivo measurement of plasma ionized calcium.

A new system for continuous in vivo measurement of ionized calcium in blood is presented. The system consists of a small chamber (400 microliter) which is thermostatized at 37 degrees C and contains a glass electrode for pH measurement and a calcium selective electrode. The chamber is mounted in an arteriovenous shunt between the femoral artery and femoral vein of heparinized (approximately 1IU/min.kg B.W.) rats. The perfusion of approximately 500 microliter/min is driven by blood pressure. The system is tested in rats undergoing acute thyroparathyroidectomy and phosphate infusion. Due to this procedure ionized calcium falls from 0.9 mmol/l (total calcium 2.0 mmol/l) to 0.35 mmol/l (total calcium 1.2 mmol/l) after 5 hours. Tetany then occurs in all animals. The system presented simplifies the measurement of ionized calcium and has the advantages of immediate and continuous recording. It is especially apt for small animals in which repeated measurements with standard techniques involve large blood losses.

Animals↗
PubMed1985

Photoreactivation of damage induced by ionizing radiation in yeast cells.

Experimental data on photoreactivation of damage induced by ionizing radiation in yeast cells are presented. The value of photoreactivation was found to be the highest for the following conditions predicted by us as optimum ones: large volume of irradiated suspension, hypoxia and high energy sparsely ionizing radiation. A comparison of data for yeast and bacterial cells shows that Cerenkov emission from ionizing radiation may produce photoreactivated pyrimidine dimers in both prokaryotic and eukaryotic cell systems.

Gamma Rays↗
PubMed1986

The carrier reorientation step in erythrocyte choline transport: pH effects and the involvement of a carrier ionizing group.

Under zero-trans conditions, the facilitated transport of choline across the erythrocyte membrane is limited by the rate of reorientation of the free carrier; as a result the pH dependence of this step can be investigated, independent of other steps in transport. It is found that as the pH declines (between 8.0 and 6.0) the rate of inward movement of the free carrier rises and the rate of outward movements falls, so that the partition of the free carrier increasingly favors the inward-facing form. When the pH of the cell interior and of the medium are varied independently, the partition responds to the internal but not the external pH. The membrane potential, which varies somewhat as the pH is altered, has no effect on the carrier partition. The analysis of the results indicates that the carrier mobility is dependent on an ionizing group of pKa 6.8, which is exposed on the cytoplasmic surface of the membrane in the inward-facing carrier; in the outward-facing carrier the ionizing group appears to be masked, in that its pKa is shifted downward by more than one unit. The observations can be explained by assuming that an ionizing group is located in the wall of a gated channel connecting the substrate site with the cytoplasmic face of the cell membrane.

Biological Transport↗
PubMed1996

Optimization of the mass spectrometric analysis of triacylglycerols using negative-ion chemical ionization with ammonia.

Conditions for the mass spectrometric analysis of triacylglycerols, via direct exposure probe, with ammonia negative-ion chemical ionization were optimized. Triacylglycerols were most favorably ionized, using the reactant gas pressure of approximately 8500 mtorr at the ion source temperature of 200 degrees C with the instrumentation used. Abundant [M-H]- ions were produced under these conditions without the formation of [M + 35]- cluster ions, which would interfere with the molecular weight region of triacylglycerols in the spectra. A rapid desorption of the sample from the probe wire is recommended, using a relatively high heating rate (approximately 40 mA s-1), to minimize thermal degradation of unsaturated molecules and the reducing effect of double bonds on the mass spectrometric response of triacylglycerols. Furthermore, the abundance of [M-H]- ion was enhanced by rapid heating, which we found to be important to improve the sensitivity. The appropriate amount of sample applied to the rhenium wire was in the region of 50-300 ng for one determination, i.e., only a few nanograms of a single triacylglycerol is required for production of a reliable spectrum. The reproducibility of the method was good as demonstrated with standards and a raspberry seed oil sample. The described mass spectrometric method is a fast and potentially useful tool for semiquantitative determination of triacylglycerol mixtures of various fats and oils. The discrimination, caused by differences in molecular size and unsaturation of triacylglycerols with 50 to 56 acyl carbons, was negligible under our optimized ionization conditions, thus, no correction factors were needed. These findings have not yet been verified with instruments in other laboratories. However, the present study shows how the analysis of triacylglycerols can be improved, regardless of the instrument, by optimization of the analytical conditions.

Ammonia↗
PubMed1989

Effect of menopause and aging on serum total and ionized calcium and protein concentrations.

The effects of menopause and aging on serum total and ionized calcium concentrations were evaluated in 402 healthy women (aged 18-71 years), of whom 83 were premenopausal and 319 postmenopausal. Serum albumin and globulin concentrations and serum pH were also measured in most of these women. Serum total but not ionized calcium concentration increased significantly at menopause. This increase in the protein-bound component of total calcium in postmenopausal women was associated with increases in mean serum globulin concentration (P = 0.03) and in serum pH (P = 0.03). Serum total calcium declined with age within the pre- and postmenopausal groups (r = -0.225, P = 0.04 and r = -0.121, P = 0.03, respectively). This was associated with an age-related decrease in serum albumin concentration in all women (r = -0.47, P less than 0.0001). Neither serum globulin concentration or pH varied with age. Thus, menopause and aging affect serum total, but not ionized calcium concentration.

Adolescent↗
PubMed1976

Patterns of total and ionized calcium and other electrolytes in plasma during and after general surgery.

Thirteen patients were studied during two hours of anaesthesia for abdmonial operations and for an hour post-operatively. Serial venous blood samples were taken for determination of plasma total and ionized calcium, acid-base variables, Na, K, Mg, PO4 total proteins and parathyroid hormone. One group of patients received 5 per cent dextrose/water and the other 5 per cent dextrose in Ringer's solution, at 250 ml per hour. Total and ionized calcium levels decreased toward the end of operation and an hour later, associated with respiratory alkalosis. Parathyroid hormone increased at the end of operation, as an effect of the decreased ionized calcium. The general effect was mild haemodilution with all the other electrolytes decreasing, as did total protein concentration.

Adult↗
PubMed2006

Spatially resolved ultra-trace analysis of elements combining resonance ionization with a MALDI-TOF spectrometer.

A combined setup for spatially resolved mass analysis of trace amounts of elements and macromolecules is presented. Using a MALDI-TOF mass spectrometer, a laser spectroscopic setup for resonant ionization of neutral atoms has been implemented. This allows for an efficient and selective detection of trace elements by means of resonance ionization mass spectrometry (RIMS). The instrumental scheme is described, and methodological developments are presented. In a first application pure, laser desorption/ionization with TOF-MS was used to measure mass distributions of cosmic nanodiamonds. For further applications regarding the spatially resolved ultra-trace analysis of elements in solid samples, an implanted target was used to characterize both laser desorption/ionization and laser desorption/resonance ionization for the detection of trace elements within. A perspective of the setup is given and future investigations are outlined.

Journal Article↗
PubMed1998

Ionization and charge-transfer: basic data for track structure calculations.

It is widely accepted that an understanding of the detailed structure of charged particle tracks is essential for interpreting the mechanistic consequences of energy deposition by high linear energy transfer (LET) radiation. The spatial relationship of events along the path of a charged particle, including excitation, ionization, and charge-transfer, govern subsequent chemical, biochemical, and biological reactions that can lead to adverse biologic effects. The determination of spatial patterns of ionization and excitation relies on a broad range of cross-section data relating the interactions of charged particles to the molecular constituents of the absorbing medium. It is important that these data be absolute in magnitude, comprehensive in scope, and reliable if accurate assessment of track structure parameters is to be achieved. Great strides have been made in the development of this database, understanding the underlying theory, and developing analytic models, particularly for interactions involving electrons and protons with atoms and molecules. The database is less comprehensive for interactions involving heavier charged particles, especially those that carry bound electrons, and for interactions in condensed phase media. Although there has been considerable progress in understanding the physical mechanisms for interactions involving fast heavy ions and atomic targets during the past few years, we still lack sufficient understanding to confidently predict cross-sections for these ions with biologically relevant material. In addition, little is known of the interaction cross-sections for heavy charged particles as they near the end of their track, i.e., for low velocity ions where collision theory is less well developed and where the particle's net charge fluctuates owing to electron capture and loss processes. This presentation focuses on the current status of ionization and charge-transfer data. Compilations, reviews, Internet sources, theoretical models, and recent data applicable to track structure calculations are discussed.

Carbon↗
PubMed1999

The track structures of ionizing particles and their application to radiation biophysics. I. A new analytical method for investigating two biophysical models.

A new approach to the interpretation of the effects of radiation on cells is described, in which sample particle tracks are constructed using a Monte Carlo computer program and the exposure of cellular targets to these tracks is simulated using a second program known as BIOPHYS. Data on the shapes and DNA contents of the cell nuclei are obtained from the literature. It is assumed that the sensitive material is DNA, and that the target is divided into cubes of approximately 2 nm (the diameter of the DNA helix) per side; the numbers of these cubes containing different numbers of ionizations are derived. Two different methods of analysing the output of BIOPHYS are described. In the first, it is assumed that lethality is caused by the occurrence of a number of ionizations equal to or greater than a certain threshold in one cube; in the second method, it is assumed that only two ionizations are required, in different parts of the cube, but that only some fraction of the cube is sensitive. These models have been applied to the interpretation of the variation of radiosensitivity with a linear energy transfer (LET) of spores of Bacillus subtilis exposed wet and dry, and good fits to the published experimental data were obtained using both models. Fits to experimental data for a range of other cell lines will be presented in a second paper.

Bacillus subtilis↗
PubMed2004

Characterization of the combined cellular survival effects of benzoquinone-ansamycins and ionizing radiation.

PURPOSE: Benzoquinone-ansamycins were the first compounds characterized with the ability to inhibit the function of heat shock protein 90 and its related family members. We investigated the composite effect of ionizing radiation and of these novel substances on the survival of malignant cells. METHODS: PC-3M prostate carcinoma cells were treated in vitro with increasing radiation doses in the presence or absence of Hsp90-active and Hsp90-inactive benzoquinone-ansamycins. Cytotoxicity was determined by the crystal violet dissolution assay. RESULTS: Twenty-four hour treatment with increasing geldanamycin doses (10 nM-1 microM) reduced cellular survival by 1.5 logs for all drug dose levels. Concomitant irradiation with a single fraction of 3 Gy reduced cellular survival by 2 logs, independently of drug dose. The treatment with 100 nM geldanamycin for 24 h combined with ionizing radiation (1-5 Gy) during the first hour of drug exposure reduced cellular survival by 1.5-2 logs depending on radiation-energy dose level, while no changes in cell survival were detectable with equimolar geldampicin, a benzoquinone-ansamycin known not to inhibit Hsp90. CONCLUSIONS: The inhibition of Hsp90 and the concomitant exposure to ionizing radiation decrease cellular survival of malignant cells. These data contribute to laying the foundation for the translational use of Hsp90 inhibitors in the multimodal therapy of cancer.

Animals↗
PubMed2005

Interaction between estrogen receptor alpha, ionizing radiation and (anti-) estrogens in breast cancer cells.

PURPOSE: Estrogen receptor alpha (ERalpha) plays a major role in breast cancer development. It acts as ligand-inducible transcription factor which determines growth, survival and differentiation of breast cancer cells. The aim of this study is to evaluate the potential interference between radiotherapy and estrogen receptor responsiveness. Materials and methods. The effect of ionizing radiation was assessed on the estrogen receptor alpha status, growth (proliferation and apoptosis) and sensitivity of MCF-7 breast cancer cells to estrogenic (17beta-estradiol (E2)), selective estrogen receptor modulator (SERM) and anti-estrogenic compounds. Results. We have observed a ligand-independent decrease in ERalpha expression after radiation, resulting from a specific reduction in mRNA level and protein synthesis. This ERalpha disappearance occurred 72 h post-irradiation at 8 Gy and decreased the transcriptional activity in ERalpha of these cells. On the other hand, E2 impedes the growth inhibitory effects (essentially on proliferation) of ionizing radiation in MCF-7 cells, which potentially decreases radiosensitivity of these cells. This effect was totally blocked by SERM and anti-estrogenic treatments. Moreover, this growth effect of concurrent anti-estrogenic drugs and ionizing radiation appeared to be strongly synergistic. CONCLUSIONS: This study may increase general comprehension of ERalpha modulation by radiotherapy and improve adjuvant therapeutic approaches based on co-administration of radiation and endocrine therapy.

Analysis of Variance↗