Heat-Induced Interactions of Bovine Serum Albumin and Immunoglobulin

Abstract

Skim milk was heated at 95°C to examine the specific interactions of bovine serum albumin and IgG using radiolabeled proteins. After heating, the milk was treated with acid and then centrifuged to separate the casein fraction from the whey. Bovine IgG transfers into the casein phase faster than does bovine serum albumin at all time periods. The heated milk was analyzed using gel filtration chromatography on Sephacryl S-300 in 6 M guanidine hydrochloride. When milk was heated for 20 min at 95°C, some of the bovine serum albumin eluted earlier than untreated bovine serum albumin, suggesting formation of complexes. Approximately half of [14C]bovine serum albumin, which was heated in bovine serum albumin solution, formed complexes and eluted earlier than the control peak. When bovine IgG was heated alone for 20 min at 95°C, all the radiolabeled IgG eluted in the void volume, indicating covalent complexes. However, heating IgG in the presence of skim milk resulted in elution of heated proteins in the same volume as control IgG. Apparently, the milk system inhibits covalent complex formation by IgG. Comparison of data from curd analysis and chromatography suggests that IgG forms noncovalent complexes with the caseins that sediment with the curd. © 1991, American Dairy Science Association. All rights reserved.