${alpha}$ and ${eta}$-subunits (ApCpnA and ApCpnB) are group II chaperonins from the hyperthermophilic archaeum Aeropyrum pernix K1, specialized in preventing the aggregation and inactivation of substrate proteins under conditions of transient heat stress. In the present study, the cooperativity of ${alpha}$- and ${eta}$-subunits from the A. pernix K1 was investigated. The ApCpnA and ApCpnB chaperonin genes were overexpressed in E. coli Rosetta and Codonplus (DE3), respectively. Each of the recombinant ${alpha}$- and ${eta}$-subunits was purified to 92% and 94% by using anionexchange chromatography. The cooperative activity between purified ${alpha}$- and ${eta}$-subunits was examined using citrate synthase (CS), alcohol dehydrogenase (ADH), and malate dehydrogenase (MDH) as substrate proteins. The addition of both ${alpha}$- and ${eta}$-subunits could effectively protect CS and ADH from thermal aggregation and inactivation at $43^{circ}C$ and $50^{circ}C$, respectively, and MDH from thermal inactivation at $80^{circ}C$C and $85^{circ}C$. Moreover, in the presence of ATP, the protective effects of ${alpha}$- and ${eta}$-subunits on CS from thermal aggregation and inactivation, and ADH from thermal aggregation, were more enhanced, whereas cooperation between chaperonins and ATP in protection activity on ADH and MDH (at $85^{circ}C$) from thermal inactivation was not observed. Specifically, the presence of both ${alpha}$- and ${eta}$- subunits could effectively protect MDH from thermal inactivation at $80^{circ}C$ in an ATP-dependent manner.