Fig. 5. Butyric acid increases the proportion of Shiga toxin endocytosed in a dynamin- and clathrin-dependent manner. HeLa and BHK control cells were grown with tetracycline for 48 hours and with and without 2 mM butyric acid (ba) for the last 24 hours. The cells were then incubated with TAG- and biotin-labelled Shiga toxin (5 ng ml^–1) (A) or transferrin (50 ng ml^–1) (B) for 15 minutes. Half of the cells were then incubated with 0.1 M MESNa for 1 hour at 0°C to remove the SS-linked biotin on the cell-surface-bound toxin before the cells we re washed and lysed. The amounts of TAG- and biotin-labelled toxin in the lysates were then measured using streptavidin beads and an Origen Analyzer, and the degree of endocytosis (as the percentage of total cell-associated protein) was calculated. The error bars represent deviations between two independent experiments.