Hydrolysis of Caprine ß-Casein by Plasmin

¹ Tecnologia dels Aliments, Centre de Referència en Tecnologia dels Aliments(CeRTA), Facultat de Veterinària, Universitat Autònoma de Barcelona, 08193 Bellaterra, Spain
² Tecnologia dels Aliments, Centre de Referència en Tecnologia dels Aliments (CeRTA), Departament d'Enginyeria Química Agrària i Tecnologia Agroalimentària (EQATA), Escola Politècnica Superior, Universitat de Girona, 17071 Girona, Spain

The proteolytic activity of plasmin on soluble caprine ßcasein (CN) was studied in 50 mM Tris-HC1 buffer, pH 8.0, at 37°C. Electrophoretic studies showed that hydrolysis of this protein results in an electrophoretic pattern that is similar to the pattern obtained from plasmin hydrolysis of bovine ß-CN (-CN and complementary N-terminal fragments), suggesting that plasmin probably attacks the same regions that are susceptible to cleavage in bovine ß-CN. As determined by SDS-PAGE, the -like components of caprine milk consisted of two fragments with relative molecular mass of 9200 and two with relative molecular mass of 21,400 that could differ in the level of phosphorylation. Apparently, the high molecular mass components are homologous to bovine ß-CN (f 29–209) (₁-CN), and the low molecular mass components are homologous to bovine ß-CN (f 106–209) and ß-CN (f 108–209) (₂- and _3--CN). Complementary N-terminal fragments had values for molecular masses in the range 13,600 to 8500 and urea-PAGE patterns that were more complex than those obtained in bovine casein because of the different phosphorylation levels in caprine ß-CN. These fragments were also present in the hydrolysate of whole caprine casein that had been treated with plasmin.

Key Words: plasmin • goat • ßbeta;-casein

Submitted on June 19, 1996
Accepted on March 20, 1997

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