Pressure effect on denaturant-induced unfolding of hen egg white lysozyme

The influence of hydrostatic pressure (less than or equal to 100 MPa) on de naturant-induced unfolding of hen egg white lysozyme was investigated by me ans of ultraviolet spectroscopy at various temperatures. Assuming a two-sta te transition model, the dependence of Gibbs free-energy change of unfoldin g on the denaturant concentration was calculated. Under applied hydrostatic pressure, these data were interpreted as suggesting that a two-state model is not applicable in a restricted temperature range; the dominant effect o f hydrostatic pressure is to affect the cooperativity in protein unfolding due to a chemical equilibrium shift in the direction of the reduction in th e system volume. The deviation from the two-state transition model appears to be rationalized by assuming that applied pressure induces an intermediat e conformation between the native and unfolded states of the protein. The i mplication of the thermodynamic stability of protein under pressure was dis cussed. (C) 2001 Wiley-Liss, Inc.