Can monomers of yeast enolase have enzymatic activity?

Using a combination of ultraviolet spectroscopy under pressure and stopped-flow kinetics under pressure, we have shown that the monomers of yeast enolase produced by hydrostatic pressure are inactive. K-eq, Delta V and Delta V-double dagger for the dissociation/inactivation produced by hydrostatic pressure have been determined under various conditions. Removing the Mg2+ from enolase, either by adding EDTA or by preparing apoenzyme, displaces the equilibrium towards monomers and decreases both Delta V and Delta V double dagger. Loss of Mg2+ contributes to the negative Delta V for dissociation; this loss occurs, at least partially, in the transition state for dissociation. Both removal of Mg(II) and dissociation of the enzyme produce major changes in the intensity of the aromatic region of the CD spectrum. We propose that these changes in the Cr) spectra reflect changes in the conformations of the "mobile loops" of enolase. The precise conformation of these loops is necessary for binding Mg2+ (and, hence, for activity) and for maintaining subunit interactions.