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  • Organic Chemistry  (7)
  • glucose  (2)
  • AbbreviationsHRPC isozyme C of horseradish peroxidase  (1)
  • 1
    Electronic Resource
    Electronic Resource
    Oscillations in cytoplasmic free calcium concentration in human pancreatic islets from subjects with normal and impaired glucose tolerance (1994)
    Springer
    Diabetologia 37 (1994), S. 1121-1131 
    Details
    ISSN: 1432-0428
    Keywords: Key words Islets of Langerhans ; glucose ; tolbutamide ; [Ca2 + ]i-oscillations ; insulin secretion.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Plasma insulin levels in healthy subjects oscillate and non-insulin-dependent diabetic patients display an irregular pattern of such oscillations. Since an increase in cytoplasmic free Ca2 + concentration ([Ca2 + ]i) in the pancreatic beta cell is the major stimulus for insulin release, this study was undertaken to investigate the dynamics of electrical activity, [Ca2 + ]i-changes and insulin release, in stimulated islets from subjects of varying glucose tolerance. In four patients it was possible to investigate more than one of these three parameters. Stimulation of pancreatic islets with glucose and tolbutamide sometimes resulted in the appearance of oscillations in [Ca2 + ]i, lasting 2–3 min. Such oscillations were observed even in some islets from patients with impaired glucose tolerance. In one islet from a diabetic patient there was no response to glucose, whereas that islet displayed [Ca2 + ]i-oscillations in response to tolbutamide, suggesting that sulphonylurea treatment can mimic the complex pattern of glucose-induced [Ca2 + ]i-oscillations. We also, for the first time, made patch-clamp recordings of membrane currents in beta-cells in situ in the islet. Stimulation with glucose and tolbutamide resulted in depolarization and appearance of action potentials. The islet preparations responded to stimulation with a number of different secretagogues with release of insulin. The present study shows that human islets can respond to stimulation with glucose and sulphonylurea with oscillations in [Ca2 + ]i, which is the signal probably underlying the oscillations in plasma insulin levels observed in healthy subjects. Interestingly, even subjects with impaired glucose tolerance had islets that responded with oscillations in [Ca2 + ]i upon glucose stimulation, although it is not known to what extent the response of these islets was representative of most islets in these patients. [Diabetologia (1994) 37: 1121–1131]
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00418376
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  • 2
    Electronic Resource
    Electronic Resource
    Oscillations in cytoplasmic free calcium concentration in human pancreatic islets from subjects with normal and impaired glucose tolerance (1994)
    Springer
    Diabetologia 37 (1994), S. 1121-1131 
    Details
    ISSN: 1432-0428
    Keywords: Islets of Langerhans ; glucose ; tolbutamide ; [Ca2+]i-oscillations ; insulin secretion
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Plasma insulin levels in healthy subjects oscillate and non-insulin-dependent diabetic patients display an irregular pattern of such oscillations. Since an increase in cytoplasmic free Ca2+ concentration ([Ca2+]i) in the pancreatic beta cell is the major stimulus for insulin release, this study was undertaken to investigate the dynamics of electrical activity, [Ca2+]i-changes and insulin release, in stimulated islets from subjects of varying glucose tolerance. In four patients it was possible to investigate more than one of these three parameters. Stimulation of pancreatic islets with glucose and tolbutamide sometimes resulted in the appearance of oscillations in [Ca2+]i, lasting 2–3 min. Such oscillations were observed even in some islets from patients with impaired glucose tolerance. In one islet from a diabetic patient there was no response to glucose, whereas that islet displayed [Ca2+]i-oscillations in response to tolbutamide, suggesting that sulphonylurea treatment can mimic the complex pattern of glucose-induced [Ca2+]i-oscillations. We also, for the first time, made patch-clamp recordings of membrane currents in beta-cells in situ in the islet. Stimulation with glucose and tolbutamide resulted in depolarization and appearance of action potentials. The islet preparations responded to stimulation with a number of different secretagogues with release of insulin. The present study shows that human islets can respond to stimulation with glucose and sulphonylurea with oscillations in [Ca2+]i, which is the signal probably underlying the oscillations in plasma insulin levels observed in healthy subjects. Interestingly, even subjects with impaired glucose tolerance had islets that responded with oscillations in [Ca2+]i upon glucose stimulation, although it is not known to what extent the response of these islets was representative of most islets in these patients.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00418376
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Metal coordination influences substrate binding in horseradish peroxidase (2000)
    Springer
    European biophysics journal 29 (2000), S. 429-438 
    Details
    ISSN: 1432-1017
    Keywords: Key words Horseradish peroxidase ; Spectral hole burning ; Protein isothermal compressibility ; Stark effect ; Porphyrin Q-band splitting ; AbbreviationsHRPC isozyme C of horseradish peroxidase ; MP mesoporphyrin IX ; MP-HRP mesoporphyrin IX horseradish peroxidase C ; MgMP ; Mg(II)-mesoporphyrin IX ; MgMP-HRP Mg(II)-mesoporphyrin IX horseradish peroxidase C ; NHA 2-naphthohydroxamic acid ; SHB spectral hole burning
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract To clarify the role of metal ion coordination in horseradish peroxidase C (HRPC), the effect of pressure and of an externally applied electric field on spectral holes was compared for both metal-free and Mg-mesoporphyrin-substituted horseradish peroxidase C (MP-HRP and MgMP-HRP), as affected by the binding of 2-naphthohydroxamic acid (NHA). The data are compared to earlier studies performed on the same derivatives. Results obtained for MP-HRP show the presence of a predominant MP tautomer, as well as that of another small population with different pocket field and isothermal compressibility (0.12 vs 0.24 GPa−1). Binding NHA induces the formation of two new almost equal populations of MP-HRP tautomer complexes and the protein compressibility in both forms is increased to 0.50 and 0.36 GPa−1. The protein structure becomes much softer than in the absence of NHA. Binding the same substrate to MgMP-HRP resulted in MgMP adopting a single conformation with no compressibility changes, while without NHA, two forms were possible. Stark effect results show charge rearrangement upon substrate binding in both cases. We propose that it is the presence of the metal that stabilizes the structure during the reorganization of the protein matrix induced by the substrate binding event. With the metal, only one conformation is adopted, without significant structural rearrangement but with charge redistribution. The dissociation constants determined for NHA binding to both derivatives and to native HRPC show that studies using mesoporphyrin and Mg-mesoporphyrin derivatives are relevant to investigating the specificity of the substrate-binding pocket in this enzyme.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002490000084
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  • 4
    Electronic Resource
    Electronic Resource
    Synthese und Reaktionsverhalten von 2-Aryl-3-chlormaleinimiden (1983)
    New York, NY : Wiley-Blackwell
    Journal für Praktische Chemie/Chemiker-Zeitung 325 (1983), S. 293-300 
    Details
    ISSN: 0021-8383
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Synthesis and Reaction Behaviour of 2-Aryl-3-chloro-maleimides2-Aryl-3-chloro-maleimides 2 are prepared by the chlorination of aryl-maleicanhydrides and aminolysis of the resulting 1-aryl-2-chloro-maleicanhydrides 1. The imide 2a is reacted with N—, S—, O— and C—nucleophiles and inorganic salts to give 2, 3-disubstituted maleimides 3-6, 9, 10, 12, condensed heterocycles 7 and maleimide dimeres 8, 13, 14.
    Additional Material: 3 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/prac.19833250216
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  • 5
    Electronic Resource
    Electronic Resource
    Reaktionen von 2-Cyan-3-methoxy-maleinimid mit methylenaktiven Verbindungen und Enaminen (1984)
    New York, NY : Wiley-Blackwell
    Journal für Praktische Chemie/Chemiker-Zeitung 326 (1984), S. 594-598 
    Details
    ISSN: 0021-8383
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Reactions of 2-Cyano-3-methoxy-maleinimide with Methylene Active Compounds and EnaminesThe vinylogous ester 1 gives with methylenactive compounds 2 carbamoylmaleinimides 3, which cyclize to pyridonimides 4. Reactions of 1 with enamines form cyanomaleinimides 6-8 and aminopyridines 11.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/prac.19843260410
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  • 6
    Electronic Resource
    Electronic Resource
    Reaktionen von 2,3-Dichlormaleinimiden mit methylenaktiven Verbindungen (1979)
    New York, NY : Wiley-Blackwell
    Journal für Praktische Chemie/Chemiker-Zeitung 321 (1979), S. 787-796 
    Details
    ISSN: 0021-8383
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Reactions of 2,3-Dichloromaleimides with Methyleneactive Compounds2,3-Dichloromaleimides 1 react with activated methylene compounds mainly under monosubstitution to give 2-6. Replacement of the second chloroatom gives 2,3-disubstituted maleimides 9-15 and stable ylides 16-27 with pyridine and triphenylphosphine, respectively. A general synthesis for such maleimid-ylides was found in a one-batch reaction from 2,3-dichloromaleimides 1 with methyleneactive compounds and pyridine or triphenylphosphine.
    Additional Material: 3 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/prac.19793210510
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  • 7
    Electronic Resource
    Electronic Resource
    Spektroskopische und polarographische Untersuchungen an 1,2-Dicarbonsäureimiden (1973)
    New York, NY : Wiley-Blackwell
    Journal für Praktische Chemie/Chemiker-Zeitung 315 (1973), S. 717-724 
    Details
    ISSN: 0021-8383
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Zum Studium des Substituenteneinflusses an 1,2-Dicarbonsäureimiden werden ihre IR-, UV-, NMR-Spektren und Polarogramme untersucht. Es wird eine lineare Beziehung der Carbonylfrequenzen, chemischen Verschiebungen und Halbstufenpotentiale zu den HAMMETT-Konstanten der Substituenten gefunden. Zur Erklärung der Substituenteneffekte an Maleinimiden ist eine gewisse Delokalisation der Imid-Ring-Elektronen anzunehmen.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/prac.19733150417
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  • 8
    Electronic Resource
    Electronic Resource
    Darstellung und Spektren der Substitutionsprodukte von 2-Chlor-maleinimiden (1974)
    New York, NY : Wiley-Blackwell
    Journal für Praktische Chemie/Chemiker-Zeitung 316 (1974), S. 113-118 
    Details
    ISSN: 0021-8383
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 2-Chlormaleinimide eignen sich als Ausgangsprodukte zur Darstellung 2-substituierter Maleinimidderivate. Durch nucleophilen Austausch lassen sich Amino-, Phenylhydrazino- und Phenoxygruppen einführen. Die unterschiedliche Donorwirkung dieser Reste auf das Maleinimidsystem kann aus den Spektren ermittelt werden.
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/prac.19743160115
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  • 9
    Electronic Resource
    Electronic Resource
    Umsetzung von 2,3-Dichlormaleinimiden mit Ethoxycarbonylmethylentriphenylphosphoran und Folgereaktionen (1979)
    New York, NY : Wiley-Blackwell
    Journal für Praktische Chemie/Chemiker-Zeitung 321 (1979), S. 797-803 
    Details
    ISSN: 0021-8383
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Reaction of 2,3-Dichloromaleimides with Ethoxycarbonylmethylenetriphenylphosphorane and Secondary Reactions2, 3-Dichloromaleimide 1a reacts with ethoxycarbonylmethylenetriphenylphosphorane under alkenylation to give 3, 4-dichlor-5-ethoxycarbonylmethylidene-3-pyrrolin-2-one 2. With N-substituted 2, 3-Dichloromaleimides 1b-1f one chloroatom is substituted to give 2-(ethoxycarbonyltriphenylphosphoranyl)-methylene-3-chloro-maleinimides 3. The reactions of 2 and 3a with various nucleophiles are investigated.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/prac.19793210511
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  • 10
    Electronic Resource
    Electronic Resource
    Elektrophile Reaktionen an der Maleinimiddoppelbindung (1984)
    New York, NY : Wiley-Blackwell
    Journal für Praktische Chemie/Chemiker-Zeitung 326 (1984), S. 401-406 
    Details
    ISSN: 0021-8383
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Electrophilic Reactions on the Maleimide Double BondThe aminosubstituted maleimides 1 are deprotonated to the anions 2, which are reacted with various electrophiles. By this way with heterocumulenes, acid chlorides and vinylogous acid chlorides the new acylated maleimides 3-6, 9, 10 are isolated. This reaction presents a method of direct acylation on the maleimide double bond.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/prac.19843260308
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