Methyl Methanethiosulfonate (MMTS)

Some methanethiosulfonates are hygroscopic and all hydrolyze in water, over a period of time, particularly in the presence of nucleophiles. They should be stored in a desiccator at minus 20 degree C and warmed up to room temperature before opening the vial. For maximum results, solutions should be made up immediately prior to use even though solutions in distilled water appear to be stable for hours at 4 degree C.
At pH 7.5 and room temperature, MTSEA hydrolyzes with a half-life of about 15 minutes, MTSET hydrolyzes with a half-life of 10 minutes, and MTSES hydrolyzes with a half-life of 20 minutes. Routinely, one can use 2.5mM MTSEA, 1mM MTSET, or 10mM MTSES, applied for 1 to 5 minutes. (MTSET is 2.5 times as reactive with small sulfhydryl compounds as is MTSEA, and 10 times as reactive as MTSES). (Stauffer and Karlin, 1994; Karlin, personal communication).
For application to Xenopus Oocytes, dissolve the compounds in 115mM NaCl, 2.5mM KCl, 1.8mM MgCl2, 10mM Hepes, pH 7.5 with NaOH. MTS reagents decompose in buffer very quickly.
•DMSO is a good solvent for the MTS reagents which are not water soluble (i.e. the non-charged MTS reagents).