SDS-PAGE and Western blotting of purified Stx2. Stx2 holotoxin was purified by affinity chromatography using a receptor analog. In panel A, a silver-stained SDS gel is shown. The cytotoxic A-subunit has a molecular mass of 32 kDa and monomeric B-subunits are separated at 7 kDa. Panel B pictures a Western blot analysis of this toxin molecule, using polyclonal rabbit anti-Stx2 antibodies. The protein preparation is free of any visible contamination.