FIG 2.

Stx2a is not released as a fully assembled AB₅ toxin. A C600::933W supernatant concentrated 25-fold was fractionated by size exclusion chromatography on a Superdex 75 column. Calculated elution volumes for Stx2a subunits (arrows) were based on size standards (light gray shading). Toxicity (solid line), plotted as percent activity loaded on the column by use of a logarithmic scale, was assessed by determining the dilution causing 50% inhibition of protein synthesis. Recovery of Stx2a A (circles) and B (squares) subunits was quantified by Western blotting, and the results are expressed as percentages of protein loaded.