Biochemical pharmacology
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Biochemical pharmacology · Oct 1985
Radiation inactivation of brain [35S]t-butylbicyclophosphorothionate binding sites reveals complicated molecular arrangements of the GABA/benzodiazepine receptor chloride channel complex.
[35S]t-Butylbicyclophosphorothionate ([35S]TBPS), a bicyclic cage convulsant, binds to the anion gating mechanism of the GABA/benzodiazepine receptor chloride channel complex. Using a carefully calibrated radiation inactivation technique, the molecular weight of [35S]TBPS binding complexes from frozen rat cerebral cortex was estimated to be 137,000 daltons. The GABA agonist muscimol reduced [35S]TBPS binding to 0-10% of the control value, in a way which is independent of the radiation dose. ⋯ The [35S]TBPS site alone in these latter conditions of membrane preparation (repeatedly frozen/washed) revealed a molecular weight of 221,000 daltons (TBPS-site + GABA receptor + unknown structures). The number of binding sites for [35S]TBPS (145 pmol/g tissue) was only slightly higher than for [3H]flunitrazepam (130 pmol/g tissue) in cerebral cortex. These results are all consonant with the conclusion that the GABA/BZ receptor chloride channel complex is composed of highly integrated multimeric subunits, tentatively accounted for by a tetramic complex of molecular weight 548,000 daltons.
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Biochemical pharmacology · Sep 1985
Comparative StudyFatty acid peptide derivatives as model compounds to protect elastin against degradation by elastases.
Peptide sequences which fit the extended binding sites of porcine pancreatic elastase and human leukocyte elastase were covalently coupled to oleic acid. These compounds behave as competitive inhibitors towards both elastases. The coupling of fatty acid moiety to the peptide greatly decreases its inhibitor constant (Ki) vs human leukocyte elastase (Ki for Oleoyl(Ala)2ProValine: 3.0 (10(-6)M). ⋯ As stoichiometric quantities of elastase (vs inhibitor) could not desorb 3H-oleoyl(Ala)2Pro-Val bound to insoluble elastin, it is postulated that oleoyl peptide derivatives may act as bifunctional agents. This contention was further strengthened by the comparison of the adsorption curves of elastase to untreated insoluble elastin and elastin saturated with oleoyl peptide derivatives respectively. It was shown finally that Oleoyl(Ala)2Pro-Valine was also capable of inhibiting elastases in their adsorbed form to insoluble elastin.
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Biochemical pharmacology · Aug 1985
Inhibition of ribonucleotide reductase and L1210 cell growth by N-hydroxy-N'-aminoguanidine derivatives.
A series of N-hydroxy-N'-aminoguanidine derivatives was studied for their effects on L1210 cell growth and ribonucleotide reductase activity. With the twelve compounds studied, there was a good correlation between the inhibition of L1210 cell growth and the inhibition of ribonucleotide reductase activity. The most potent compound required concentrations of only 1.4 and 2 microM for 50% inhibition of L1210 cell growth and ribonucleotide reductase activity respectively. ⋯ Iron-chelating agents did not either increase or decrease the inhibition caused by the N-hydroxy-N'-aminoguanidine derivatives. No evidence was obtained that these derivatives selectively inactivated one of the subunits of ribonucleotide reductase. These compounds appear to inhibit ribonucleotide reductase by a mechanism different from hydroxyurea or the thiosemicarbazone derivatives.