Pressure-induced Reversible Dissociation of Enolase

A study of the polarization of the intrinsic fluorescence and the fluorescence of dansyl conjugates of enolase shows that an increase in hydrostatic pressure, in the range of 1 bar-3 kbar, promotes the dissociation of this protein into dimers. The dissociation of oligomeric proteins under pressure is predicted to be a general phenomenon by a model that assumes the existence of small "free volumes" at the intersubunit boundaries. The same model predicts a dependence of the standard volume change in the dissociation reaction upon the pressure, owing to the additional surface compressibility of the monomers, and numerical analysis of the results clearly shows that dependence for enolase. For a midpoint dissociation pressure of 1.5 kbar the standard volume change in the dissociation reaction is delta V p0 = -65 +/- 8 mL mol-1 and the dependence of the volume change upon pressure (dVp0/dp) is approximately -30 mL mol-1 kbar-1. The reversibility of the pressure effects is shown to be better than 95% by either polarization or fluorescence spectrum recovery. The pressure perturbation of the fluorescence polarization is a method of general applicability to studies of protein aggregation, and it can be also of value in characterizing the effect of ligands on the aggregation of oligomeric proteins.