The SDS-PAGE-Western blot (A), native-PAGE-Western blot (B) and CBS activity (C) of the CBS constructs of wild type and the R266K mutant. The crude extracts (soluble fraction, 30 μg) were separated either in a 10% Tris-HCl gel using reducing denaturing conditions (A) or in a 4–15% Tris-HCl gel under native conditions (B), transferred to a polyvinylidene difluoride membrane and probed with monoclonal anti-CBS antibody (Abnova). Arrows designate the GST-CBS fusion protein, 6xHis-tagged CBS protein and native tetramers, respectively.