The ATPase activity of DnaK, the 70-kDa chaperone of Escherichia coli, is stimulated by an unfolded protein. However, the stimulation of the DnaK ATPase by unfolded bovine pancreatic trypsin inhibitor can only be observed at low DnaK protein concentrations. At higher DnaK concentrations, the ATPase activity of DnaK cannot be stimulated by the addition of unfolded bovine pancreatic trypsin inhibitor. This is a consequence of the autostimulation of the DnaK ATPase at higher DnaK concentrations. The autostimulation of DnaK is reflected by a non-linear dependence of ATP hydrolysis on DnaK concentration. Furthermore, DnaK exists as a mixture of monomers and dimers in equilibrium, and the dimers dissociate into monomers in the presence of ATP.
