EMCS and its water-soluble analog Sulfo-EMCS are heterobifunctional cross-linkers that contain N-hydroxysuccinimide
(NHS)ester and maleimide groups that allow covalent conjugation of amine- and sulfhydryl-containing molecules.NHS
esters react with primary amines at pH 7-9 to form amide bonds,while maleimides react with sulfhydryl groups at pH
6.5-7.5 to form stable thioether bonds.In aqueous solutions,hydrolytic degradation of the NHS ester is a competing
reaction whose rate increases with pH.The maleimide group is more stable than the NHS-ester group but will slowly
hydrolyze and also lose its reaction specificity for sulfhydryls at pH values>7.5.For these reasons,conjugation
experiments involving these cross-linkers are usually performed at pH 7.2-7.5,with the NHS-ester(amine-targeted)
reaction being accomplished before or simultaneous with the maleimide(sulfhydryl-targeted)reaction.
应用
EMCS is not directly water-soluble and must be dissolved first in an organic solvent such
as dimethylsulfoxide(DMSO)or dimethylformamide(DMF);subsequent dilution into aqueous reaction buffer is generally
possible,and most protein reactants will remain soluble if the final concentration of organic solvent is less than 10%.