The pressure-induced, reversible inactivation of mouse brain enolases

The three isozymes of mouse brain enolase (alpha alpha, alpha gamma and gamma gamma) were subjected to pressures between 160 MPa and 380 MPa. Enzymatic activity 2 min after the pressure exposure was used to monitor pressure-induced changes in the physical state of the protein. Pressure caused a reversible inactivation of all three forms; alpha alpha showed a continual inactivation with increasing pressure whereas the inactivation curves for alpha gamma and gamma gamma were biphasic. P1 2 for alpha alpha was 190 MPa, for alpha gamma 210 MPa and for gamma gamma 280 MPa. Volume changes associated with this inactivation were calculated for all three forms of the enzyme; delta V0 varied from -150 ml mol-1 to -170 ml mol-1, assuming a model in which there was no change in the aggregation state of the enzyme, or from -230 ml mol-1 to -250 ml mol-1 assuming that the enzyme dissociated on exposure to pressure. The half-time for reactivation was measured as a function of the concentration of enzyme; the results are consistent with an inactivation that is due to dissociation of the dimeric enzyme into monomers.