MODIFICATIONS OF HIGH-ORDER STRUCTURES UPON HEATING OF BETA-LACTOGLOBULIN - DEPENDENCE ON THE PROTEIN-CONCENTRATION

A study on the concentration dependence of the modifications ensuing f rom thermal treatment of bovine beta-lactoglobulin was carried out by using a combination of techniques. Heat-induced changes in tertiary st ructure were monitored by intrinsic tryptophan fluorescence, while mod ifications in protein surface hydrophobicity were studied both during their occurrence and at equilibrium by using the fluorescent hydrophob ic probe 1, 8-anilinonaphthalenesulfonate. The association equilibria in the heated and cooled protein and the stabilization of aggregates b y intermolecular disulfides were studied by gel permeation chromatogra phy and nonreducing, denaturing electrophoresis. Results indicate that irreversible modification of the tertiary structure is not concentrat ion dependent, while the temperature required for the occurrence of pr otein swelling, the initial step in the formation of associated forms of the protein, increases with the protein concentration. Stabilizatio n of aggregates by intermolecular disulfides was dependent on concentr ation only at temperatures below 75 degrees C.