Figure 3. Cpa complex assembly and ATPase activity are strongly influenced by pH and ionic strength.

(A) ATPase activity is enhanced with increasing pH and decreasing KCl concentration. The activity was measured at 28°C using 1.5 µM ^RerCpa (protomer). For readability reasons, the errors of the measurements are not shown – in all cases the error did not exceed 5% of the measured value. (B) Increasing ionic strength slows down Cpa complex formation. Assembly reactions were prepared using 9 µM ^RerCpa in a buffer containing increasing KCl concentrations (0–400 mM), incubated at 18°C and injected onto a SEC column at the indicated time points.