Suramin greatly inhibits Hsp104 refolding activity.

<p>(<b>A</b>) Urea-denatured firefly luciferase aggregates were incubated for 90 min at 25°C with Hsp104 (1 µM hexamer) plus 1∶1 mixtures of ATP and ATPγS and varying concentrations of GdmCl. Luciferase reactivation was then determined and converted to % WT disaggregase activity in the presence of ATPγS: ATP. Values represent mean ±S.D. (<i>n</i> = 3–6). (<b>B</b>) Reactions were performed as in (<b>A</b>) except varying concentrations of Suramin were used. Values represent mean ±S.D. (<i>n</i> = 6–10). (<b>C</b>) Half maximal inhibitory concentration (IC₅₀) for Suramin-mediated inhibition of Hsp104. IC₅₀ was calculating by fitting luciferase-refolding data at different Suramin concentrations. (<b>D</b>) Reactions were performed as in (<b>A</b>) except that 1∶1 mixtures of ATP and ATPγS were replaced with Hsp70 (1 µM) and Hsp40 (1 µM) plus ATP. The Hsp104 alone condition (yellow bars) was carried out with 1∶1 mixtures of ATP and ATPγS as in (<b>A</b>). Each condition is normalized to the refolding activity in each corresponding condition in the absence of inhibitor.