To understand how molecular damage under harsh environmental conditions can be controlled, we investigated the properties of ATPase activity of the chaperonin molecular machinery from the hyperthermophilic archaeon Pyrococcus furiosus (PfCPN). PfCPN ATPase activity depended on K+ and Mg2+ and its optimal pH was 7.5. PfCPN had almost no ADPase activity. ADP strongly competitively inhibited PfCPN ATPase activity. Inhibition of PfCPN ATPase decreased its chaperonin activity in protecting lysozyme from heat-induced inactivation.