MOLECULAR MODIFICATIONS OF BETA-LACTOGLOBULIN UPON EXPOSURE TO HIGH-PRESSURE

Irreversible modifications in tertiary structure, surface hydrophobici ty, and association state of beta-lactoglobulin were studied after exp osure to high pressure (600 and 900 MPa) of solutions of the protein a t neutral pH and at different concentrations. Only minor irreversible structural modifications were evident even for treatments as intense a s 15 min at 900 MPa. The occurrence of irreversible modifications was time-progressive at 600 MPa but was complete within 2 min at 900 MPa. The irreversibly modified protein was soluble, but some covalent aggre gates were formed. Formation of aggregates increased with increasing p rotein concentration and was prevented by blocking the free thiol moie ty in each beta-lactoglobulin monomer. Results are discussed in light of their practical relevance, and a unifying denaturation mechanism is envisaged for beta-lactoglobulin. In the proposed mechanism, release of monomers represents one of the earliest events, while association o f transiently modified monomers stabilizes the denatured forms of the protein.