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  • 1
    Electronic Resource
    Electronic Resource
    Alkylation of ionic mercury to methylmercury and dimethylmercury by methylcobalamin: Simultaneous determination by purge-and-trap GC in line with FTIR (1993)
    New York, NY [u.a.] : Wiley-Blackwell
    Applied Organometallic Chemistry 7 (1993), S. 487-493 
    Details
    ISSN: 0268-2605
    Keywords: Mercury ; methylation ; methylcobalamine ; Vitamin B12 ; Fourier transform IR spectroscopy ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A new approach was used to determine the reaction products of methylcobalamin and ionic mercury: purge-and-trap gas chromatography in line with Fourier transform infrared spectroscopy (PT GC/FTIR). This technique simultaneously and specifically determines the spectrum of dimethylmercury (DMeHg) and methylmercury produced by the reaction. No interference from other known organic mercury species could be detected. The method is different from others because it does not require solvent extraction of the organomercurials from aqueous solution, but relies on immediate volatilization from the reaction vessel by addition of 100 μl of 10 mM NaBH4. The sample was purged with nitrogen for 10 min. The volatile species of mercury were trapped in a column at -120°C, injected into the gas chromatograph and detected by FTIR. The efficiency of DMeHg and MeHg formation depended on different parameters: pH, temperature, reaction time, and the methylcobalamin/ionic mercury ratio. The initial reaction product was MeHg which was further transformed to DMeHg. The first methylation rate was two times faster than the second. MeHg formed first, reaching a maximum at higher temperatures (28°C and 37°C) and later decreasing as DMeHg formed. At lower temperatures (20°C) the rate of MeHg formation was slower, being similar to the formation rate of DMeHg. Different species of inorganic mercury such as HgSO4, Hg(NO3)2, Hg(SCN)2, HgCl2 and Hgl2 were used to study differences in methylation by methylcobalamin under standard conditions of acidity, temperature and cofactor Hg(II) ratio.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aoc.590070707
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  • 2
    Electronic Resource
    Electronic Resource
    Endothelin stimulates phosphatidic acid formation in cultured rat mesangial cells: Role of a protein kinase C-regulated phospholipase D (1992)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Cellular Physiology 150 (1992), S. 578-585 
    Details
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: We have previously reported that endothelin-1 stimulates phospholipase C-in-duced hydrolysis of phosphatidylinositol-4, 5-bisphosphate, Other signal transduction pathways that hydrolyze alternative phospholipids through phospholipase D may also mediate endothelin-stimulated cellular responses. We initially evaluated endothelin-dependent generation of 32P-phosphatidic acid as an indirect indication of phospholipase D activity in rat mesangial cells. Endothelin (10-7M) induced an elevation of phosphatidic acid that was maximal at 15 min and persisted upward of 60 min. Pretreatment with the diacylglycerol-kinase inhibitor, R59022, did not reduce formation of endothelin-stimulated 32P-phosphatidic acid, demonstrating that the sequential actions of phospholipase C/diacylglycerol kinase do not contribute to endothelin-stimulated phosphatidic acid formation. We next conclusively identified a role for phospholipase D in the generation of phosphatidic acid by assessing the formation of 3H-phosphatidylethanol from 3H-alkyl lyso glycerophosphocholine and exogenous ethanol. Endothelin stimulated 3H-alkyl phosphatidylethanol formation in the presence but not the absence of 0.5% ethanol. Also, endothelin induced a concomitant elevation of 3H-alkyl-phosphatidic acid that was significantly reduced when the cells were exposed to exogenous ethanol, reflecting the formation of phosphatidylethanol. In addition, endothelin stimulated the release of 3H-choline and 3H-ethanolamine, demonstrating that additional phospholipids may serve as substrates for phospholipase D. Phorbol esters and synthetic diglycerides mimicked the effects of endothelin to stimulate phospholipase D and inhibitors of protein kinase C significantly reduced endothelin-stimulated phospholipase D. In addition, endothelin did not stimulate phosphatidylethanol formation in protein kinase C down-regulated cells. The calcium ionophore, ionomycin, did not stimulate phospholipase D and mesangial cells pretreated with BAPTA to chelate cytosolic calcium did not show a diminished endothelin-stimulated phospholipase D. Thus these data demonstrate that mesangial cells possess a protein kinase C-regulated phospholipase D activity that can be stimulated with endothelin.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcp.1041500319
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