TAILIEUCHUNG - Báo cáo Y học: Proteolysis of bovine b-lactoglobulin during thermal treatment in subdenaturing conditions highlights some structural features of the temperature-modified protein and yields fragments with low immunoreactivity

Bovineb-lactoglobulin was hydrolyzed with trypsin or chymotrypsin in the course of heat treatment at 55, 60 and 65°C at neutral pH. At these temperaturesb-lactoglobulin undergoes signi®cant but reversible structural changes. In the conditions used in the present study,b-lactoglobulinwas virtually insensitive to proteolysis by either enzyme at room temperature, but underwent extensive proteolysis when either proteasewas present during the heat treatment. | Eur. J. Biochem. 269 1362-1372 2002 FEBS 2002 Proteolysis of bovine b-lactoglobulin during thermal treatment in subdenaturing conditions highlights some structural features of the temperature-modified protein and yields fragments with low immunoreactivity Stefania iametti1 Patrizia Rasmussen1 2 Hanne Frokiffir2 Pasauale Ferranti2 Francesco Addeo3 B F MB B 4 M M MB MM MB MM B MM B B B B BB B BB MB B B B B MM B B B B BB B B MB B B M MB B B FB BB mm BB BB B BB B mb B B BB B B m B B B BB B B M MB BB M MB B M BB BB MB MB and Francesco Bonomi1 1 Dipartimento di Scienze Molecolari Agroalimentari University of Milan Italy 2Biocentrum Technical University of Denmark Lyngby Denmark 3Istituto di Scienze dell Alimentazione CNR Avellino Italy Bovine b-lactoglobulin was hydrolyzed with trypsin or chymotrypsin in the course of heat treatment at 55 60 and 65 C at neutral pH. At these temperatures b-lactoglobulin undergoes significant but reversible structural changes. In the conditions used in the present study b-lactoglobulin was virtually insensitive to proteolysis by either enzyme at room temperature but underwent extensive proteolysis when either protease was present during the heat treatment. High-temperature proteolysis occurs in a progressive manner. Mass spectrometry analysis of some large-sized breakdown intermediates formed in the early steps of hydrolysis indicated that both enzymes effectively hydrolyzed some regions of b-lactoglobulin that were transiently exposed during the physical treatments and that were not accessible in the native protein. The immunochemical properties of the products of b-lactoglobulin hydrolysis were assessed by using various b-lactoglobulin-specifc antibodies and most epitopic sites were no longer present after attack of the partially unfolded protein by the two proteases. Keywords bovine b-lactoglobulin limited proteolysis partial unfolding thermal treatment reduced immunoreactivity. The globular protein b-lactoglobulin is found in the whey

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