Activation parameters for the spontaneous and pressure-induced phases of the dissociation of single-ring GroEL (SR1) chaperonin

We investigated the dissociation of single-ring heptameric GroEL (SR1) by high hydrostatic pressure in the range 0.5-3.0 kbar. The kinetics were studied as a function of temperature in the range 15-35 degreesC. The dissociation processes at each pressure and temperature showed biphasic behavior. The slower rate (k(1,obs)) was confirmed to be the self-dissociation of SR1 at any specific temperature at atmospheric pressure. This dissociation was pressure independent and followed concentration-dependent first-order kinetics. The self-dissociation rates followed normal Eyring plots (in k(1,obs)/T vs. 1/T) from which the free energy of activation (DeltaG(not equal) = 22 +/- 0.3 kcal mol(-1)), enthalpy of activation (DeltaH(not equal) = 18 +/- 0.5 kcal mol(-1)), and entropy of activation (DeltaS(not equal) = -15 +/- 1 kcal mol(-1)) were evaluated. The effect of pressure on the dissociation rates resulted in nonlinear behavior (In k(2,obs) vs. pressure) at all the temperatures studied indicating that the activation volumes were pressure dependent. Activation volumes at zero pressure (V-0(not equal)) and compressibility factors (beta(not equal)) for the dissociation rates at the specific temperatures were calculated. This is the first systematic study where the self-dissociation of an oligomeric chaperonin as well as its activation parameters are reported.