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  • 1985-1989  (4)
  • 1980-1984  (1)
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  • 1
    Digitale Medien
    Digitale Medien
    Differential Sensitivity of Basal and Opioid-Stimulated Low Km GTPase to Guanine Nucleotide Analogs (1986)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neurochemistry 47 (1986), S. 0 
    Details
    ISSN: 1471-4159
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Medizin
    Notizen: Abstract In membranes derived from NG108–15 cells, the opioid peptide [D-Ala2,D-Leu5]enkephaIin (DADLE) stimulates a low Km GTPase. The nucleotide analogs guanosine 5′-O-(2-thio)diphosphate (GDPβS), guanosine 5′-(β,γ-imi-do)triphosphate [Gpp(NH)p] and guanosine 5′-O-(3-thio)-triphosphate (GTPγS) inhibit the basal enzymatic activity with the order of potency GTPγS 〉 Gpp (NH)p 〉 GDPβS. In the presence of DADLE, the inhibition isotherms of GDPβS and Gpp(NH)p are shifted to the right five- and fourfold, respectively, compared to the inhibition observed in the absence of DADLE. In contrast, the IC50 of GTPγS for inhibiting the enzyme is reduced by 55% in the presence of the opioid. Both Gpp(NH)p and GTPγS produce a concentration-dependent increase in the Km(app) of GTPase. without affecting its Vmax, indicating a competitive inhlbi-tion. However, the replots of Km(app) versus inhibitor concentration are hyperbolic, suggesting a partial type of inhibi-tion. Both Gpp(NH)p and GTPγS, but not GTP, induce an increase in the EC50 of DADLE for stimulating GTPase These findings indicate that the basal and the opioid-stimu-lated low Km GTPase differ in their respective sensitivities to inhibition by guanine nucleotide analogs.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1111/j.1471-4159.1986.tb00766.x
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  • 2
    Digitale Medien
    Digitale Medien
    Opioid Receptors of Neuroblastoma Cells Are in Two Domains of the Plasma Membrane that Differ in Content of G Proteins (1989)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neurochemistry 52 (1989), S. 0 
    Details
    ISSN: 1471-4159
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Medizin
    Notizen: Abstract: Opioid receptors of NG 108–15 cell membranes are distributed in two membrane fractions sedimenting at 20,000 g (P2) and 200,000 g (P3). The number of receptors is identical in P2 and P3, but in P2 all sites are present in one high-affinity state (2 nM), whereas in P3 60% of these receptors display lower affinity (150 nM). Upon addition of GTP or pretreatment with pertussis toxin, 80% of the sites exist in low affinity in both P2 and P3. Therefore, the effect of GTP and pertussis toxin on agonist binding appears to be smaller in P2 than in P3. In contrast, sodium inhibits agonist binding in P2 and P3 to the same extent and with identical potency. Opioid-mediated stimulation of GTPase is much greater in P2 than in P3, whereas inhibition of adenylate cyclase does not differ in the two fractions. Using site-specific antibodies and pertussis toxin-catalyzed ADP-ribosylation, we found that the amount of G proteins in P3 is only 30–50% of that in P2. Treatment of intact cells with the hydrophilic protein-modifying agent sulfosuccinimido-biotin results in biotinylation of proteins from both fractions and in a similar reduction of opioid binding in P2 and P3. Likewise, exposure of intact cells to the alkylating opioid antagonist, chlornaltrexamine, produces identical degrees of receptor inactivation in P2 and P3. The rate of in vivo pertussis toxin-mediated modification of G proteins is not different in the two fractions. We conclude from these data that (1) a larger proportion of receptors is uncoupled from G proteins in P3 than in P2; (2) the effects of GTP and Na+ on opioid receptor binding can be attributed to different membrane components; and (3) receptors in P3 appear to be present in the plasma membranes and, thus, do not represent internalized receptors.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1111/j.1471-4159.1989.tb09164.x
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  • 3
    Digitale Medien
    Digitale Medien
    Dimeric tetrapeptide enkephalins display extraordinary selectivity for the δ opiate receptor (1982)
    [s.l.] : Nature Publishing Group
    Nature 297 (1982), S. 333-335 
    Details
    ISSN: 1476-4687
    Quelle: Nature Archives 1869 - 2009
    Thema: Biologie , Chemie und Pharmazie , Medizin , Allgemeine Naturwissenschaft , Physik
    Notizen: [Auszug] A series of dimeric tetrapeptide enkephalins have been synthesized by a two-step coupling procedure: cross-linking of Boc-Phe-OH with NH2-(CH2)n-NH2 (where w=2-12), followed by elongation with Boc-Tyr-D-Ala-Gly-OH. Purity was confirmed by mass spectrometry, amino acid analysis and TLC. [D-Ala2, ...
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1038/297333a0
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  • 4
    Digitale Medien
    Digitale Medien
    Effects of sodium and GTP on the binding kinetics of [3H]diprenorphine in NG 108-15 cell membranes (1986)
    Springer
    Naunyn-Schmiedeberg's archives of pharmacology 334 (1986), S. 444-451 
    Details
    ISSN: 1432-1912
    Schlagwort(e): Neuroblastoma x glioma cells ; Diprenorphine ; Dissociation rate constant ; Sodium ; GTP ; Pertussis toxin ; NEM
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Summary Equilibrium binding isotherms of [3H]diprenorphine in membranes from NG 108-15 cells are consistent with a homogenous population of binding sites. Upon addition of Na+, Mg2+ and GTP, only a 2-fold reduction in affinity with a minor decrease in the number of sites is observed. Dissociation curves of [3H]diprenorphine, however, are clearly biphasic: in the absence of Na+, Mg2+ and GTP, 80% of the bound ligand dissociates slowly with at 1/2 of 100 min, and only 20% rapidly (t 1/2 4.5 min). In the presence of Mg2+, nearly all the binding is found in the slowly dissociating form. Upon the addition of either Na+ or GTP, 20–30% of the binding dissociates more rapidly. The rate constant of the rapidly dissociating form generated by Na+, however, is 2.5 times greater than that induced by the presence of GTP. Thus, the addition of both, Na+ and GTP, converts about 80% of the receptor into a very fast dissociating form (t 1/2 1.7 min). Exposure of intact cells to pertussis toxin (10 ng/ml) or treatment of membranes with N-ethyl maleimide (500 μM), strongly reduces the proportion of the slowly dissociating component. Following these treatments, the effect of GTP is reduced or abolished, but that of Na+ remains unaffected. We conclude from these data that the effects of Na+ and GTP are not only distinct in site but also in mechanism of action and that there are three forms of opioid receptors that can be differentiated by their kinetic properties. The slowly dissociating receptor form requires a functional N unit.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00569384
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  • 5
    Digitale Medien
    Digitale Medien
    Binding characteristics of a series of dimeric tripeptide enkephalins for δ opiate receptors in rat brain and NG108-15 cells (1989)
    Chicester [u.a.] : Wiley-Blackwell
    Journal of Molecular Recognition 2 (1989), S. 127-131 
    Details
    ISSN: 0952-3499
    Schlagwort(e): Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Medizin
    Notizen: The N-terminal tripeptide enkephalin analogue, Tyr-D-Ala-Gly, was dimerized at the C-terminus systematically with a series of α,ω-diaminoalkanes, NH2—(CH2)n—NH2 (n = 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, and 22). The binding affinities of dimers for δ opiate receptors in rat brain were evaluated and compared with those for δ receptors in NG108-15 cells. Although the monomeric tripeptide amide was almost inactive, dimers showed a dramatic increase in binding affinity (8-900 times). The enhancement of affinity was apparently related to the number of methylene chains in the crosslinking spacer moiety, and it was maximal at n = 14-18 in the rat brain. In NG cells the activity increased progressively from n = 2 to n = 22 without reaching any apparent peak. These results suggest that δ receptors in rat brain and NG cells may have slight structural differences.
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/jmr.300020305
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