Mechanism of action of the redox affinity reagent [(trimethylammonio)methyl]catechol.
The synthesis of 4- and 5-hydroxy-3-[(trimethylammonio)methyl]catechol (4- and 5-HTMC) was carried out to examine their proposed involvement as intermediates in the spontaneous redox-dependent half-of-sites inactivation of neurotoxin binding sites in the nicotinic acetylcholine receptor (nAcChR) mediated by the parent compound 3-[(trimethylammonio)methyl]catechol (TMC) [Nickoloff et al. (1985) Biochemistry 24, 999-1007]. Oxidation of 4- and 5-HTMC occurred with sodium periodate with facile conversion to the corresponding p-quinones which were intercepted with thiols and cyclopentadiene. Both 4- and 5-HTMC inactivated neurotoxin binding in the nAcChR in a time course and over a concentration range consistent with their involvement as intermediates in the TMC redox-dependent inactivation of neurotoxin ([125I]-alpha-bungarotoxin) binding sites. Rapid concentration-dependent inactivation of neurotoxin sites occurred over a 10-1000 microM range and was resistant to further inactivation after 50% loss of available toxin binding sites on the nAcChR. Both 4- and 5-HTMC inactivated nAcChR neurotoxin sites much more rapidly and efficiently than was observed previously with TMC. The apparent binding constants for 4- and 5-HTMC with the nAcChR, calculated from their concentration-dependent inactivation behavior toward toxin binding sites, were Kd = 224 +/- 98 and 39 +/- 17 microM, respectively. The observed results and the redox potentials (vs Ag/AgCl reference electrode) measured by cyclic voltammetry at pH 1.8 for TMC (719 mV) and the 4- and 5-HTMC derivatives (519 and 443 mV, respectively) supported the previously proposed mechanism for inactivation of the nAcChR by TMC.(ABSTRACT TRUNCATED AT 250 WORDS)
Department of Medicinal and Biological Chemistry, College of Pharmacy, University of Toledo, Ohio 43606.
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Gu
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Lee
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Kirchhoff
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Manzey
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Hudson
D001548:Benzalkonium Compounds / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology; D001665:Binding Sites; D002038:Bungarotoxins / Q000378:metabolism; D002396:Catechols / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology*; D004229:Dithiothreitol / Q000494:pharmacology; D004563:Electrochemistry; D007202:Indicators and Reagents; D007700:Kinetics; D009682:Magnetic Resonance Spectroscopy; D010084:Oxidation-Reduction; D011809:Quinones / Q000378:metabolism; D011978:Receptors, Nicotinic / Q000187:drug effects* / Q000378:metabolism; D013053:Spectrophotometry; D013816:Thermodynamics
D001548:Benzalkonium Compounds; D002038:Bungarotoxins; D002396:Catechols; D007202:Indicators and Reagents; D011809:Quinones; D011978:Receptors, Nicotinic; C088430:4-hydroxy-3-((trimethylammonio)methyl)catechol; C088431:5-hydroxy-3-((trimethylammonio)methyl)catechol; C036022:3-trimethylaminomethylcatechol; D004229:Dithiothreitol