Figure 1.

Measurement of changes in free energy during the allosteric transition of GroEL. In the absence of ATP, GroEL is mainly in the TT state. In the presence of low concentrations of ATP, the equilibrium is shifted toward the TR state (L₁ = [TT]/[TR]). Higher concentrations of ATP further shift the equilibrium toward the RR state (L₂ = [TR]/[RR]). For simplicity, we designate by R the ATP-bound rings in both the TR and RR states although their conformation may differ. The difference in free energy between the TR and TT states of wild-type GroEL is given by ΔG_TR-TT = −RTlnL₁. Likewise, the difference in free energy between the RR and TR states of wild-type GroEL is ΔG_RR-TR = −RTlnL₂. The difference in free energy between the TR and TT states of wild-type GroEL and a mutant [designated by prime (′)] is given by ΔΔG_TR-TT = −RTln(L₁/L₁′). Likewise, the difference in free energy between the RR and TR states of wild-type GroEL and a mutant is given by ΔΔG_RR-TR = −RTln(L₂/L₂′).