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  • Analytical Chemistry and Spectroscopy  (147)
  • Life and Medical Sciences  (104)
  • 1990-1994  (224)
  • 1980-1984
  • 1965-1969  (27)
  • 1990  (224)
  • 1969  (27)
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  • 1990-1994  (224)
  • 1980-1984
  • 1965-1969  (27)
Year
  • 1
    Electronic Resource
    Electronic Resource
    The use of dynamically programmed scans to generate parent-ion tandem mass spectra with the ion-trap mass spectrometer (1990)
    New York, NY : Wiley-Blackwell
    Rapid Communications in Mass Spectrometry 4 (1990), S. 108-113 
    Details
    ISSN: 0951-4198
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: A method is described whereby, under software control, the scan function employed to collisionally excite ions in an ion-trap mass spectrometer is regulated so as to obtain parent ion (fixed product) tandem mass spectral data. At the same time, constant neutral-loss information is also provided. Key features are the automatic ‘intelligent’ selection of parent ions from observation of the initial mass spectrum and the scanning of the applied ‘tickle’ frequency in order to locate the precise resonance points for excitation of these ions. Results for the model compounds perfluorotributylamine (‘FC43’) and n-butylbenzene are reported and complicating effects such as the unimolecular decay of the precursor ion species and charge exchange between product ions and the original sample material are discussed.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/rcm.1290040404
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  • 2
    Electronic Resource
    Electronic Resource
    A detailed study of the characteristics of the ion-trap mass spectrometer using dynamically programmed scans (1990)
    New York, NY : Wiley-Blackwell
    Rapid Communications in Mass Spectrometry 4 (1990), S. 415-417 
    Details
    ISSN: 0951-4198
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: The aims of the investigation were to use the method of dynamically programmed scans to study in detail some tandem mass spectrometric characteristics of the ion-trap mass spectrometer and then to use the programs to investigate the possibility of performing benchtop gas chromatography/tandem mass spectrometry experiments on the standard instrument. In particular we have examined the effect of applying a DC ramp during the ‘tickle’ period as a means of broadening the range of resonant frequencies, thereby facilitating the tuning required to effect excitation.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/rcm.1290041015
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  • 3
    Electronic Resource
    Electronic Resource
    A simple model for calculating residential 60-Hz magnetic fields (1990)
    New York, NY [u.a.] : Wiley-Blackwell
    Bioelectromagnetics 11 (1990), S. 283-296 
    Details
    ISSN: 0197-8462
    Keywords: grounding currents ; ELF ; exposure assessment ; Life and Medical Sciences ; Occupational Health and Environmental Toxicology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Physics
    Notes: A model is presented that permits the calculation of densities of 60-Hz magnetic fields throughout a residence from only a few measurements. We assume that residential magnetic fields are produced by sources external to the house and by the residential grounding circuit. The field from external sources is measured with a single probe. The field produced by the grounding circuit is calculated from the current flowing in the circuit and its geometry. The two fields are combined to give a prediction of the total field at any point in the house. A data-acquisition system was built to record the magnitude and phase of the grounding current and the field from external sources. The model's predictions were compared with measurements of the total magnetic field at a single location in 23 houses; a correlation coefficient of .87 was obtained, indicating that the model has good predictive capability. A more detailed study that was carried out in one house permitted comparisons of measurements with the model's predictions at locations throughout the house. Again, quite reasonable agreement was found. We also investigated the temporal variability of field readings in this house. Daily magnetic field averages were found to be considerably more stable than hourly averages. Finally, we demonstrate the use of the model in creating a profile of the magnetic fields in a home.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bem.2250110405
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  • 4
    Electronic Resource
    Electronic Resource
    Changes in the mitochondrial calcium influx and efflux properties are responsible for the decline in sperm calcium during epididymal maturation (1990)
    New York, NY [u.a.] : Wiley-Blackwell
    Molecular Reproduction and Development 25 (1990), S. 186-194 
    Details
    ISSN: 1040-452X
    Keywords: Intracellular calcium ; Intracellular pH ; Mitochondira ; Epididymal sperm ; Bovine ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology
    Notes: This study was undertaken to determine the role of calcium ion, a key regulator of the intensity and form of motility in mature demembranated sperm, in the development of motility during passage through the bovine epididymis. Cellular calcium levels in bovine caput and cauda epididymal spermatozoa were measured with three different techniques. 45Ca2+ uptake measurements revealed that net calcium uptake and Ca2+-Ca2+ exchange in caput spermatozoa were about 2 to 3 times higher than in caudal spermatozoa. Intracellular free calcium determination with the calcium fluorophore Fura 2 showed that the levels were 6 times higher in caput spermatozoa. The values for caput and caudal sperm were 875±55 nM (n = 15) and 155±6 nM (n = 24), respectively. Total cellular calcium levels quantitated by atomic absorption were 626±30 (n = 48) and 304±19 (n = 46) ng/108 sperm in caput and caudal epididymal sperm, respectively. At least one of the reasons for the high calcium content of caput epididymal sperm is the result of a higher rate and extent of mitochondrial calcium accumulation in caput compared to caudal sperm. Mitochondrial calcium uptake rates measured in digitonin permeabilized cells revealed uptake rates 2- to 3-fold higher in caput compared to caudal sperm. However, mitochondrial calcium efflux rates were identical in caput and caudal epididymal sperm. The efflux rates in both cell types were unaffected by external sodium levels but were found to be proportional to pH. Alkalinization or acidification of internal pH of intact sperm resulted in a corresponding lowering or elevation of cytoplasmic free calcium levels. We propose that external calcium has access to sperm only via the mitochondria (Vijayaraghavan and Hoskins: Cell Calcium 10:241-253, 1989) and that this mitochondrial calcium is subsequently redistributed into the cytoplasmic space as a function of the internal pH. We document for the first time that changes in mitochondrial calcium handling properties are important in epididymal sperm maturation and suggest that the acquisition of sperm motility in the epididymis could be related to these changes in sperm calcium handling properties.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrd.1080250212
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  • 5
    Electronic Resource
    Electronic Resource
    Alternative driving functions for a collision quadrupole (1990)
    New York, NY : Wiley-Blackwell
    Rapid Communications in Mass Spectrometry 4 (1990), S. 440-441 
    Details
    ISSN: 0951-4198
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: The work presented here introduces a new variable parameter in the design of quadrupole collision cells. A brief summary of the mathematical theory is given to demonstrate how the maximum value of the parameter q may be altered. This is achieved through changing the driving function used for the rod potentials.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/rcm.1290041021
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  • 6
    Electronic Resource
    Electronic Resource
    Theoretical studies of ion trajectories in quadrupole systems (1990)
    New York, NY : Wiley-Blackwell
    Rapid Communications in Mass Spectrometry 4 (1990), S. 442-446 
    Details
    ISSN: 0951-4198
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: A brief introduction to the mathematical theory of quadrupole systems is given and the configuration of hyperbolic and circular cross-section rods is considered. Application of the theory of electrostatics to the latter case indicates that multipole contributions to the field occur which influence the ion trajectories. We have considered motion in the x-z plane of a static quadrupole (DC-only) for the simplest case of a 1:1 combination of quadrupole and dodecapole contributions. The quadrupole contribution to ion motion is simple harmonic and may be described as a sine function, whereas the dodecapole contribution may only be obtained by solving the appropriate elliptic integral. This solution gives rise to a sine (amplitude) or sn function. In the case of collision cells (RF-only) we have attempted to solve the Mathieu equation both analytically and numerically. Both stable and unstable trajectories may be calculated from these solutions and are presented in various formats. Some consideration is also given to the problems of collisional interaction and the associated difficulties likely to be encountered when the study is expanded to include this phenomenon.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/rcm.1290041022
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  • 7
    Electronic Resource
    Electronic Resource
    Measurement of stable isotopic enrichment of underivatized acetate by gas chromatography/mass spectrometry: Application to in vivo estimation of acetate production (1990)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 19 (1990), S. 554-558 
    Details
    ISSN: 1052-9306
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In order to assess endogenous and colonic production of acetate, we have developed an assay for determining the isotopic enrichment of plasma acetate using gas chromatography/mass spectrometry (GC/MS). Acidified, deproteinized plasma (200 μl) was extracted into ethyl ether, and the ether phase was then injected into a gas chromatograph/mass spectrometer fitted with a 30 m × 0.252 mm i.d. capillary column (temperature program 50-245°C at 10°C min-1). Using electron impact GC/MS and selected ion monitoring, peak areas of ions with m/z 60 and 61 (M + 1) were determined. Triplicate extractions of enriched plasma samples (mol.% excess 1.38-1.5%) resulted in a coefficient of variation of 1.6-5.9%. Unenriched plasma samples were found to have an enrichment close to theoretical natural abundance, and analysis of our (1-13C)acetate tracer (99 at.% excess) revealed an ion at m/z 61 and no ion at m/z 60. To verify accuracy, we conducted an in vivo isotope dilution study. In a 1-month-old piglet, fasted for 24 h, changing the rate of a 4 h infusion (mmol h-1) of (1-13C)acetate from 0.141 to 0.282 doubled the isotope enrichment (2.08 x) of the second plateau. The rate of appearance of acetate was 26.0 μmol kg-1 min -1, which is comparable to that reported in fasting sheep.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bms.1200190906
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  • 8
    Electronic Resource
    Electronic Resource
    Form and function of protein assemblies (1969)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Cellular Physiology 74 (1969), S. 239-240 
    Details
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Assemblies of protein molecules represent a fundamental level of biological organization. The dynamic behavior of these systems-including both the assembly process and functional rearrangements-may be accounted for by the specificity of the protein interactions, which depend on environmental conditions. Analysis of the self-assembly of virus particles has established that the design of an ordered structure can be built into the specific bonding properties of the constituent proteins. Any structure which can change its state of organization is, by definition, polymorphic. The distinctive aspect of polymorphism in protein structures, contrasted with nonliving states of matter, is that the molecular design has been selected to carry out a function and that this function is part of an integrated system. The differences in molecular conformation and arrangement in all polymorphic structures-for example, allosteric enzymes or ice crystals-depend on the intrinsic interaction properties of the molecules themselves. The structures of ice and water illustrate relations between specificity and polymorphism which are relevant to the form and function of protein assemblies.Two types of polymorphism can be distinguished: modal polymorphism, which is externally moderated, as in phase transitions between different crystals forms; and positional polymorphism, which is internally moderated, as in the different disposition of identical molecules within a single crystal lattice. Positional polymorphism, exemplified by the quasi-equivalent bonding of icosahedral virus coat proteins and the different arrangement of myosin and paramyosin at the center and polar portions of the bipolar filaments, results from specific interactions that are not compatible with a strictly equivalent packing of identical molecules. The structural rearrangements in muscle contraction and the switching between the oxy and deoxy forms of hemoglobin represent the formation of different structures in response to altered external conditions. The different structural states of many protein assemblies are characterized by conserved connections which may be regarded as providing the framework for functional rearrangements. The types of polymorphism displayed by hemoglobin, virus, and muscle proteins demonstrate the relevance of the simple view that the function of a protein is determined by the potential structures it can form.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcp.1040740427
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  • 9
    Electronic Resource
    Electronic Resource
    Stimulation of plasma membrane and matrix vesicle enzyme activity by transforming growth factor-β in osteosarcoma cell cultures (1990)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Cellular Physiology 145 (1990), S. 200-206 
    Details
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Transforming growth factor-β (TGFβ) serves an important role in extracellular matrix formation by stimulating the production of numerous extracellular matrix proteins by connective tissue cells and by osteoblasts or bone-forming cells. TGFβ has been shown to stimulate alkaline phosphatase (ALPase) activity in the rat osteoblast-like osteosarcoma cell line ROS 17/2.8. Previous studies have shown that this enzyme is elevated during calcification of bone and that it is enriched in matrix vesicles, an extracellular organelle associated with initial hydroxyapatite formation. To test the hypothesis that TGFβ plays a role in regulating mineral deposition in the matrix, the effects of TGFβ on ALPase and phospholipase A2, two enzymes associated with mineralization, were examined. ROS 17/2.8 cells were cultured at high and low density with recombinant human TGFβ (0.1-10 ng/ml) to examine the influence of cell maturation on response to TGFβ. Maximal stimulation of ALPase activity in the low density cultures was seen at 5 ng/ml; in high-density cultures, there was further stimulation at 10 ng/ml. There was a dose-dependent increase in ALPase activity seen in the matrix vesicles and plasma membranes in both types of cultures. Matrix vesicle ALPase exhibited a greater response to factor than did the plasma membrane enzyme. However, in low density cultures, the two membrane fractions exhibited a parallel response with greatest activity consistently in the matrix vesicles. There was a dose-dependent increase in phospholipase A2-specific activity in the plasma membranes and matrix vesicles of both high- and low-density cultures. In agreement with previous studies, TGFβ inhibited cellular proliferation 50%. The results show that addition of TGFβ stimulates the activity of enzymes associated with calcification. The effect of TGFβ is dependent on the stage of maturation of the cell. This study indicates that TGFβ may play an important role in induced bone formation, calcification, and fracture repair in addition to its role in promoting chondrogenesis.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcp.1041450203
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  • 10
    Electronic Resource
    Electronic Resource
    Osteoblasts display receptors for and responses to leukemia-inhibitory factor (1990)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Cellular Physiology 145 (1990), S. 110-119 
    Details
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Specific binding of leukemia-inhibitory factor (LIF) to osteoblasts, but not multinucleated osteoclasts, was demonstrated by receptor autoradiography by *using cells isolated from newborn rat long bones. The clonal rat osteogenic sarcoma cells, UMR 106-06, which have several phenotypic properties of osteoblasts, expressed 300 LIF receptors per cell, with an apparent KD of 60 pM. Treatment of calvarial osteoblasts or UMR 106-01 cells with LIF resulted in a dose-dependent inhibition of plasminogen activator (PA) activity. Both calvarial osteoblasts and osteogenic sarcoma cells were shown by Western blotting and reverse fibrin autography to produce plasminogen activator inhibitor-1 (PAI-1), the production of which was increased by LIF treatment. Northern blot analysis revealed that LIF treatment resulted in a rapid (peak 1 hour), dose-dependent increase in mRNA for PAI-1. LIF treatment of the preosteoblast cell line, UMR 201, enhanced the alkaline phosphatase response of these cells to retinoic acid. Each of the osteoblast-like cell types (calvarial osteoblasts, UMR 106-06, and UMR 201) was shown to produce LIF by bioassay and, by using the polymerase chain reaction (PCR), was shown to express low levels of mRNA for LIF. These data establish that cells of the osteoblast lineage are targets for LIF action. The reported anabolic effects of this cytokine on bone formation in vivo could be related to inhibition of protease activity. LIF may be an important paracrine modulator in bone, or perhaps an autocrine one, based on the evidence for its production by osteoblasts and osteoblast-like cells.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcp.1041450116
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