IRREVERSIBLE HIGH-PRESSURE INACTIVATION OF BETA-GALACTOSIDASE FROM KLUYVEROMYCES-LACTIS - COMPARISON WITH THERMAL INACTIVATION

High hydrostatic pressure and high temperature are both shown to induc e inactivation of Kluyveromyces lactis beta-galactosidase in deionised water and their respective effects are compared. These two physical p arameters lead to similar inactivation kinetics which can be suitably represented by series-type models. The plot of half-lives as a functio n of pressure is close to the same plot towards temperature, Thus, the same inactivation rate constant can be obtained in two:different ways : an increase in pressure at room temperature or an increase in temper ature at atmospheric pressure (e.g. 125 MPa at 25 degrees C or 45 degr ees C at 0.1 MPa for a k(1), value about 28 x 10(-2) min(-1)). When be ta-galactosidase was prepared in 0.1 M potassium phosphate buffer pH 7 .3, its stability in extreme conditions of pressure as at high tempera ture was strongly enhanced. This stabilizing effect of the buffer was essentially attributed to a pH-effect by comparison with the behaviour of the enzyme in a similar buffer but with a 10-fold lower ionic stre ngth. (C) 1998 Elsevier Science B.V; All rights reserved.