(A) purification of rhBSSL by heparin-chromatography with HiTrap Heparin HP. 25ml milk whey was loaded onto a HiTrap Heparin HP 5ml column. F, the flow through; P, the elution peak. (B) 12% SDS-PAGE and Coomassie blue staining of the flow-through and elution peak. (C) Purification of rhBSSL from the first chromatographic step by Superdex 200 gel filtration chromatography. The P fraction from first step was loaded on the column after being desalted by 10mM sodium phosphate buffer (pH 7.0). P1, impurities and P2, purified rhBSSL. (D) Purity of rhBSSL (P2) was examined by SDS-PAGE and silver staining. 1, 6 μg rhBSSL; 2, 12 μg rhBSSL; 3, 10 μg rhBSSL.