Reassembly of CtxB as function of pH.
A. Reassembly of CtxB into SDS stable pentamer. Equal amount of reassembled CtxB was applied on each lane of a SDS-PAGE. CtxB reassembled for 0 min and 30 min at pH 7.0 (lanes 2 and 3), or for 30 min at pH 6.0 (lane 4) or and at pH 5.0 (lane 5). Lane 1 is the native CtxB5. Molecular weight standards are indicated in kDa on the left of the gel. The respective apparent positions of the native CtxB pentamer and of the CtxB monomer are indicated on the right of the gel. B. Reassembly of CtxB into species capable of recognizing GM1. CtxB5 (○) was treated at pH 1.0 for 15 min and subsequently diluted to a final concentration of 8.6 µM in McIlVaine buffers at indicated pH. The samples were incubated for 30 min at 23°C and analyzed by GM1-Elisa. The results of three independent experiments are shown as a mean ± S.D.