MBS and its water-soluble analog Sulfo-MBS 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
MBS 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%.