HYDROLYSIS OF BETA-LACTOGLOBULIN BY THERMOLYSIN AND PEPSIN UNDER HIGH HYDROSTATIC-PRESSURE

Hydrolysis of beta-lactoglobulin with thermolysin and pepsin at pressures ranging between 0.1 and 350 MPa showed a significant increase of cleavage rates. Pressure-induced changes of susceptibility to hydrolysis of beta-lactoglobulin proteolytic sites were also observed. The pressure, raised to 200 MPa, accelerates the hydrolysis of beta-lactoglobulin by thermolysin and changes obtained peptide profiles. Initially, higher pressure makes the N-terminal, and to a smaller extent, C-terminal peptide fragments of beta-lactoglobulin molecule, move susceptible to removal by thermolysin. This indicates combined influence of pressure-induced thermolysin activation and par- tial unfolding of beta-lactoglobulin by compression at neutral pHs. The rates of hydrolysis of beta-lactoglobulin by pepsin (negligible at 0.1 MPa) are increased considerably with pressure up to 300 MPa. The susceptibility of beta-lactoglobulin proteolytic sites to peptic cleavage remains constant over all the studied pressure range. The lack of significant qualitative changes in the peptic peptide profiles produced at different pressures and at clearly pressure-dependent rates points to negative reaction volume changes as the major factor in peptic hydrolysis of beta-lactoglobulin under high pressure Thus the beta-lactoglobulin molecule resists pressure-induced unfolding in acid pHs and yields to it in neutral pHs. (C) 1995 John Wiley & Sons, Inc.