Proteolysis of bovine βâlactoglobulin during thermal treatment in subdenaturing conditions highlights some structural features of the temperatureâmodified protein and yields fragments with low immunoreactivity
2002
Iametti, Stefania | Rasmussen, Patrizia | Frøkiær, Hanne | Ferranti, Pasquale | Addeo, Francesco | Bonomi, Francesco
Bovine βâlactoglobulin was hydrolyzed with trypsin or chymotrypsin in the course of heat treatment at 55, 60 and 65â°C at neutral pH. At these temperatures βâlactoglobulin undergoes significant but reversible structural changes. In the conditions used in the present study, βâlactoglobulin was virtually insensitive to proteolysis by either enzyme at room temperature, but underwent extensive proteolysis when either protease was present during the heat treatment. Highâtemperature proteolysis occurs in a progressive manner. Mass spectrometry analysis of some largeâsized breakdown intermediates formed in the early steps of hydrolysis indicated that both enzymes effectively hydrolyzed some regions of βâlactoglobulin that were transiently exposed during the physical treatments and that were not accessible in the native protein. The immunochemical properties of the products of βâlactoglobulin hydrolysis were assessed by using various βâlactoglobulinâspecific antibodies, and most epitopic sites were no longer present after attack of the partially unfolded protein by the two proteases.
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