Recombinant Protein-L produced in E.Coli is a single non-glycosylated polypeptide chain fused with a Cys at C-terminus. Protein-L is comprised of 5 IgG-binding regions of protein L (B1-B2-B3-B4-B5) containing 366 amino acids in total and having a molecular mass of 40.6kDa, however, it migrates with an apparent molecular mass of 46kDa on SDS-PAGE. Cell wall binding region, cell membrane binding region and albumin binding region have been eliminated from the recombinant Protein-L to guarantee the maximum specific IgG binding.