Purity >98% by SDS-PAGE and HPLC, MW: 33.5 kDa. SPA-Cys Recombinant produced in E.Coli is a single non-glycosylated polypeptide chain with a Cys on C-terminus. ?SPA-Cys is comprised of 5 IgG-binding domains E-D-A-B-C aligned in series containing 297 amino acids and having a molecular mass of 33.5kDa containing little or no carbohydrate.?Cell wall binding region, cell membrane binding region and albumin binding region were removed to ensure the highest specific IgG binding.