High hydrostatic pressure stabilized galactose oxidase (GaOx) at 70.0-80.0°C against thermal inactivation. The pseudo-first-order rate constant of inactivation k inact decreased by a factor of 8 at 80°C and by a factor of 44 at 72.5°C. The most pronounced effect of pressure was at the lowest studied temperature of 70.0°C with an activation volume of inactivation ΔV ‡ of 78.8 cm 3 mol -1 . The optimal pressure against thermal inactivation was between 200 and 300 MPa. Unlike other enzymes, as temperature increased the ΔV ‡ of inactivation decreased, and as pressure increased the activation energy of inactivation E ai increased. Combining the results for GaOx with earlier research on the pressure-induced stabilization of other enzymes suggests that ΔV ‡ of inactivation correlates with the total molar volume of cavities larger than ~100 Å 3 in enzyme monomers for enzymes near the optimal pH and whose thermal unfolding is not accompanied by oligomer dissociation.
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