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)
Symmetrically bis-catechol-substituted analogues (1 and 2, respectively) of hexamethonium and decamethonium were synthesized and investigated as redox-activated affinity reagents toward the neurotoxin-binding sites of the nicotinic acetylcholine receptor (nAcChR), purified from Torpedo californica electroplax. These reagents bound to nAcChR with Kd = 1.8 x 10(-8) and 2.3 x 10(-7) M for 1 and 2, respectively. In the presence of a metal, Fe(II)/Fe(III), and peroxide, both reagents produced a rapid and efficient half-of-sites inactivation of neurotoxin-binding sites in the nAcChR in a concentration-dependent manner, which paralleled the extent of receptor binding of the reagents. In the absence of Fe(II)/Fe(III) peroxide, redox-dependent inactivation occurred for both 1 and 2 more slowly and only at concentrations much higher (10(3)-10(4) times) than those necessary to produce significant binding to nAcChR. However, receptor inactivation in the absence of added metal peroxide was still more efficient for 1 and 2 than observed previously for [(trimethylammonio)methyl]catechol (3), the prototypic redox-dependent affinity reagent after which 1 and 2 were patterned. Thus, the new reagents reported are expected to provide more efficient and selective conditions for redox-dependent inactivation at nAcChR and other macromolecular sites to which such reagents may be directed.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.