MTSET (chloride) is a methanethiosulfonate (MTS), a sulfhydryl-reactive compound that forms mixed disulfide linkages. It is a positively charged sulfhydryl-specific reagent that reacts with substituted cysteines. It can provide functional information about relative positions of amino acids within a protein and can be used to probe binding site electrostatic interactions.[1][2][3]
Reference:
[1]. O'Reilly, J.P., and Shockett, P.E. Time- and state-dependent effects of methanethiosulfonate ethylammonium (MTSEA) exposure differ between heart and skeletal muscle voltage-gated Na+ channels. Biochem. Biophys. Acta. 1818(3), 443-447 (2012).
[2]. Li, R.A., Tsushima, R.G., Kallen, R.G., et al. Pore residues critical for μ-CTX binding to rat skeletal muscle Na+ channels revealed by cysteine mutagenesis. Biophys. J. 73(4), 1874-1884 (1997).
[3]. Lang, R.J., Harvey, J.R., and Mulholland, E.L. Sodium (2-sulfonatoethyl) methanethiosulfonate prevents S-nitroso-L-cysteine activation of Ca2+-activated K+ (BKCa) channels in myocytes of the guinea-pig taenia caeca. Br. J. Pharmacol. 139(6), 1153-1163 (2003).