Formation of new protein structures in heated mixtures of BSA and alpha-lactalbumin

The heat-induced protein-protein interactions of alpha-lactalbumin (alpha-L a) and bovine serum albumin (BSA), dispersed in a pH 6.8, 10% whey protein concentrates (WPC) permeate, were followed using alkaline and sodium dodecy l sulfate (SDS) 1D and 2D polyacrylamide gel electrophoresis (PAGE) and siz e-exclusion high-performance liquid chromatography (SE-HPLC). Heated (75 de grees C) 5% BSA solution contained large disulfide-bonded BSA aggregates, a lthough some monomer BSA (SDS-monomeric BSA) could be dissociated from the aggregates by SDS. In contrast, similarly heated alpha-La solutions contain ed small quantities of several monomeric forms of alpha-La and dimeric alph a-La but no large aggregates. When 10% solutions of 1:1 (w/w) mixtures of a lpha-la and BSA were heated, large disulfide-bonded aggregates and SDS-mono meric BSA and alpha-La were present. However, heated 2% mixtures contained more modified alpha-La monomers, alpha-La-dimers, and alpha-La-trimers, few er large disulfide-bonded aggregates, and less SDS-monomeric alpha-La or BS A. These results suggest that BSA forms disulfide-bonded aggregates that co ntain available thiol groups that can catalyze the formation of differently structured alpha-La monomers, dimers, higher polymers, and adducts of alph a-La with BSA.