Maleimide-Activated Streptavidin is for directly preparing streptavidin-protein conjugates with proteins, peptides and other molecules that contain a free sulphhydryl (-SH) group. Streptavidin has been maleimide-activated using Sulpho-SMCC, a heterobifunctional crosslinker that contains an N-hydroxysuccinimide ester and a maleimide group. The activated streptavidin presents an available maleimide group that reacts with sulphhydryl-containing molecules.