BARIC OLIGOMERIZATION IN ALPHA-LACTALBUMIN BETA-LACTOGLOBULIN MIXTURES/

The influence of high pressure on alpha-lactalbumin(ALA)/beta-lactoglo bulin (BLG) mixtures of various compositions was studied at pH 8.5 (50 mM Tris) by gel-permeation chromatography and sodium dodecyl sulfate- polyacrylamide gel electrophoresis (SDS-PAGE) without 2-mercaptoethano l. High-molecular-weight disulfide-linked protein oligomers formed at a pressure of 10 kbar (1000 MPa) if the weight fraction of BLG (W-BLG( 0)) in the protein mixture exceeded 0.2. The maximum yield of these ol igomers, of the order 80-85%, was observed at W-BLG(0) greater than or equal to 0.4. Conversion of both proteins in the oligomers was roughl y the same. The estimates of the oligomerization yield obtained by gel -permeation chromatography and SDS-PAGE agreed well. SDS-PAGE results indicated that the oligomerization of pressure-denatured ALA and BLG i s driven by thiol <-> disulfide exchange in which the free thiol group of BLG acts as an initiator.