Succinimidyl-4-(N-maleimidomethyl)cyclohexane-1-carboxylate (SMCC), an N-hydroxysuccinimide ester derived from 4-(N-maleimidomethyl)cyclohexane-1-carboxylic acid, is a non-cleavable and membrane permeable crosslinker. It is used for enzyme labelling of antibodies - both enzyme and antibody specificity can be preserved; for creation of specific bioconjugates via one- or two-step crosslinking reactions; for creation of sulfhydryl-reactive, maleimide-activated carrier proteins for coupling haptens. SMCC conjugation occurs via a maleimide group that is sulfhydryl (thiol; -SH) reactive and a NHS ester group that is amine reactive and forms stable, covalent protein crosslinks. SMCC crosslinker must be dissolved in an organic solvent, such as DMSO or DMF, and then can be added to an aqueous crosslinking reaction. SMCC crosslinking reagent is permeable across the lipid bilayer of the cell membrane and can be used to crosslink intracellular proteins and peptides.