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  • 1
    Electronic Resource
    Electronic Resource
    Kinetic Modulation by GABAergic Agents of High- and Low-Affinity Binding of [3H]Methyl β-Carboline-3-Carboxylate (1988)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neurochemistry 50 (1988), S. 0 
    Details
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: The kinetics of dissociation of [3H]methyl β-carboline-3-carboxylate (β-CCM) binding was studied in a synaptosomal membrane preparation of rat cerebral cortex. Dissociation was biphasic: a faster phase (10–30% contribution) was followed by a slower phase. Picrotoxin pre-treatment at 22°C enhanced the equilibrium binding of [3H]β-CCM. The half-life of the slower phase of β-CCM dissociation (tII1/2) was increased by 60 μM picrotoxin from 1.7 min to 3.3 min. The dissociation of [3H]β-CCM was identical when initiated by an excess of either diazepam or β-CCM. Quasi-equilibrium Scatchard analysis of [3H]β-CCM binding was performed by a kinetic separation of the rapid and slow phases of dissociation. The slow and rapid phases represented β-CCM binding sites of high and low affinity, respectively. The dissociation of [3H]β-CCM (control tII1/2= 2.0 min) was decelerated by the γ-aminobutyric acid (GABA) antagonist 3–α-hydroxy-16-imino-5β-17-azaandrostan-11-one (R 5135) (tII1/2= 2.5 min) and accelerated by GABA (tII1/2= 1.6 min). GABA inhibited both high- and low-affinity β-CCM bindings.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1471-4159.1988.tb02489.x
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  • 2
    Electronic Resource
    Electronic Resource
    Thermodynamics and kinetics of t-butylbicyclophosphorothionate binding differentiate convulsant and depressant barbiturate stereoisomers acting via GABAA ionophores (1996)
    Springer
    Naunyn-Schmiedeberg's archives of pharmacology 353 (1996), S. 306-313 
    Details
    ISSN: 1432-1912
    Keywords: Key words GABAA receptor-ionophore complex ; Dissociation of [35S]TBPS binding ; Barbiturate stereoisomers ; Arrhenius analysis ; Thermodynamics of barbiturate binding ; Electrophysiology of GABAA-ionophores.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract  The temperature dependence of [35S]-t-butylbicyclophosphorothionate (TBPS) binding to the convulsant sites of the GABAA receptor complex was studied in membrane preparations of rat forebrain. Although specific [35S]TBPS binding was maximal around 20° C, the rate constants of dissociation decreased monotonously between 37° C and 2° C. The displacing potencies of the convulsant S(+) enantiomer of 1-methyl-5-phenyl-5-propyl-barbituric acid (MPPB) (IC50=1250±30 μM) and the depressant R(−) MPPB (IC50=310±5 μM) did not show significant changes between 19° C and 37° C. Therefore barbiturate binding seems to be driven by entropic, rather than enthalpic changes. An excess of MPPB enantiomers elicited accelerated and polyphasic dissociations of [35S]TBPS as compared to the monophasic dissociation by TBPS. Arrhenius analysis was applied to the measurable initial rate constants of dissociation. Arrhenius plots were linear between 2° C and 37° C. Activation parameters were similar when [35S] TBPS dissociation was triggered by the convulsants TBPS and S(+) MPPB. It can be attributed to similar conformations of the closed ionophore complex. In contrast, the depressant R(−) MPPB strongly decreased the activation energy of TBPS dissociation from the open ionophore ternary complex. In whole-cell patch-clamp experiments R(−) MPPB, but not S(+) MPPB, elicited chloride currents in rat primary cortical cultures with an EC50 value of 560±30 μM and a Hill coefficient of 2.9±0.2. These currents were similar to those elicited by GABA and blocked by TBPS. A kinetic scheme is proposed for the dissociation of TBPS and to explain the different effects of MPPB enantiomers. Submillimolar R(−) MPPB is supposed to bind to (about three) barbiturate sites on GABAA-ionophores and to open them in a cooperative manner to result in a decreased activation energy for accelerated displacement of convulsant binding.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00168633
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  • 3
    Electronic Resource
    Electronic Resource
    Methiodide of the GABA antagonist (+)-bicuculline is levorotatory (1989)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 1 (1989), S. 178-179 
    Details
    ISSN: 0899-0042
    Keywords: CD spectra ; optical rotation ; phthalideisoquinoline base and salts ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The appearance of positive charge on the nitrogen moiety of phthalideisoquinoline alkaloids brings about a strong change in the intensities of CD Cotton effects. Hence the optical rotations of enantiomeric salts and their parent base of identical configuration are often of opposite sign. Thus, the name (+)-bicuculline-methiodide for the methiodide salt of (+)-bicuculline is false.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chir.530010214
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  • 4
    Electronic Resource
    Electronic Resource
    Stereoselective effect of warfarin and bilirubin on the binding of 5-(o-chlorophenyl)-1,3-dihydro-3-methyl-7-nitro-2H-1,4- benzodiazin-2-one enantiomers to human serum albumin (1990)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 2 (1990), S. 161-166 
    Details
    ISSN: 0899-0042
    Keywords: protein binding ; affinity chromatography ; resolution ; allosteric interaction ; increased enantioselectivity ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The binding of the title benzodiazepine enantiomers and its modulation by warfarin and bilirubin were studied by chromatography on human serum albumin (HSA) immobilized on Sepharose 4B, and also by a combination of ultrafiltration and circular dichroism (UF-CD) methods. In the absence of warfarin and bilirubin the binding of the benzodiazepine was not stereoselective. (S)-Benzodiazepine and (S)-warfarin mutually increased the binding of each other, while the binding of (R)-benzodiazepine was preferentially enhanced on HSA saturated with bilirubin.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chir.530020307
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  • 5
    Electronic Resource
    Electronic Resource
    Stereoselective effect of phenprocoumon enantiomers on the binding of benzodiazepines to human serum albumin (1992)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 4 (1992), S. 21-23 
    Details
    ISSN: 0899-0042
    Keywords: protein binding ; affinity chromatography ; resolution ; allosteric interaction ; increased enantioselectivity ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The effect of phenprocoumon enantiomers on the stereoselective binding of 3-substituted 1,4-benzodiazepines to human serum albumin (HSA) was studied by chromatography on HSA-Sepharose column. (S)-Phenprocoumon exerts stereoselective allosteric interaction on the binding of benzodiazepines. The structural requirements of enhanced stereoselectivities are similar to those found previously with (S)-warfarin.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chir.530040106
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  • 6
    Electronic Resource
    Electronic Resource
    Stereoselective distribution of acenocoumarol enantiomers in human plasma: Chiral chromatographic analysis of the ultrafiltrates (1993)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 5 (1993), S. 346-349 
    Details
    ISSN: 0899-0042
    Keywords: stereoselective protein binding ; chiral liquid chromatography ; human serum albumin ; α1-acid glycoprotein ; anticoagulant ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Stereoselectivities for the binding of rac-acenocoumarol to human serum albumin (HSA), α1-acid glycoprotein (AGP), and human plasma were determined by chiral HPLC analysis of the ultrafiltrates on a Chiral-AGP column. The results confirmed the previously detected inverse stereoselectivities; for HSA the ratio of the enantiomeric constants was KR/KS ∼ 2, while for AGP it was KR/KS ∼ 0.3. In plasma the contribution of HSA dominates, although in pathological states, elevated AGP levels may compensate for stereoselective distribution. © 1993 Wiley-Liss, Inc.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chir.530050513
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  • 7
    Electronic Resource
    Electronic Resource
    The role of configuration and conformation in the binding of 2,3-benzodiazepines to human serum albumin (1989)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 1 (1989), S. 271-275 
    Details
    ISSN: 0899-0042
    Keywords: HSA-affinity chromatography ; interconverting conformers ; conformational selectivity ; conformational diastereomers ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 2,3-Benzodiazepines containing a centre of asymmetry at C-5 possess both central and helical chiralities, and the solution of their racemates contains four molecular species. The binding of these compounds to human serum albumin (HSA) was studied by affinity chromatography. The binding strength depended both on the steric orientation of the 5-ethyl substituent and on the conformation of the diazepine ring. Conformation P (defined by the positive sign of C-1-N-2-N-3-C-4 torsion angle) is favoured, while the quasiaxial orientation -of the 5-ethyl substituent is not favoured by the albumin molecule.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chir.530010405
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