Streptavidin is a crystalline protein isolated from the bacterium Streptomyces avidinii and possesses biotin-binding ability. The dissociation constant (Kd) of the biotin-streptavidin complex is about ~1015 M.Streptavidin has an immunosuppressive role. The Streptavidin protein solution contains 50mM Tris-HCl pH-8 & 0.15M NaCl.