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Formation of New Protein Structures in Heated Mixtures of BSA and α-Lactalbumin

2000; American Chemical Society; Volume: 48; Issue: 5 Linguagem: Inglês

10.1021/jf990736j

1520-5118

Palatasa Havea, Harjinder Singh, Lawrence K. Creamer,

Protein Interaction Studies and Fluorescence Analysis

The heat-induced protein−protein interactions of α-lactalbumin (α-La) and bovine serum albumin (BSA), dispersed in a pH 6.8, 10% whey protein concentrates (WPC) permeate, were followed using alkaline and sodium dodecyl sulfate (SDS) 1D and 2D polyacrylamide gel electrophoresis (PAGE) and size-exclusion high-performance liquid chromatography (SE-HPLC). Heated (75 °C) 5% BSA solution contained large disulfide-bonded BSA aggregates, although some monomer BSA (SDS-monomeric BSA) could be dissociated from the aggregates by SDS. In contrast, similarly heated α-La solutions contained small quantities of several monomeric forms of α-La and dimeric α-La but no large aggregates. When 10% solutions of 1:1 (w/w) mixtures of α-La and BSA were heated, large disulfide-bonded aggregates and SDS-monomeric BSA and α-La were present. However, heated 2% mixtures contained more modified α-La monomers, α-La-dimers, and α-La-trimers, fewer large disulfide-bonded aggregates, and less SDS-monomeric α-La or BSA. These results suggest that BSA forms disulfide-bonded aggregates that contain available thiol groups that can catalyze the formation of differently structured α-La monomers, dimers, higher polymers, and adducts of α-La with BSA. Keywords: Homogeneous aggregates; heterogeneous aggregates; disulfide bond interchange; α-lactalbumin−BSA adducts; α-lactalbumin dimers; α-lactalbumin trimers; thermal denaturation; disulfide-bonded aggregates; size-exclusion high-performance liquid chromatography; two-dimensional polyacrylamide gel electrophoresis