7 20 mM Tris-HCl, 20 mM Imidazole, 0.5 M NaCl, pH 8.0 2 Column chromatography gel filtration column chromatography (GE Healthcare UK Ltd., HiLoad 10/30 Superdex 200 pg) 120 _ crib220u270rib220u62091i _ 1.5 _