Monospecificity of the antibodies to bovine alpha s1-casein fragment 140-149: application to the detection of bovine milk in caprine dairy products.

Comparison of the primary sequences of bovine, ovine and caprine alpha s1-casein shows a deletion of eight amino acid residues in the ovine casein region 141-148, which is identical in the bovine and caprine proteins except for a single difference in position 148 (Q or E). Polyclonal antibodies raised in rabbits against the bovine casein sequence 140-149 (QELAYFYPEL) appeared monospecific for bovine alpha s1-casein, since no antibody-antigen complex was formed with homologous ovine or caprine proteins. These antibodies remained unable to recognize the caprine sequence in the native protein even after extensive tryptic proteolysis. The lack of immunoreactivity of the antibodies against synthetic caprine alpha s1-casein peptide 138-149 (VNQELAYFYPQL) suggested that the glutamic acid residue in position 148 is essential for the antigenic character of the bovine peptide. From these observations, the use of these antibodies for the detection and quantitation of bovine milk present in ovine dairy products could be extended to caprine products.