OCCURRENCE OF 5 ALPHA(S1)-CASEIN VARIANTS IN OVINE MILK

Five ovine alpha(s1)-casein variants (A-E) were identified in an Itali an population sample using gel electrophoresis at alkaline pH, gel iso electric focusing, two dimensional gel electrophoresis, and immunoblot ting with polyclonal antibodies against alpha(s1)-casein. Each casein sample produced two peaks by fast reversed-phase HPLC. Gel isoelectric focusing and electrospray mass spectrometry were used to demonstrate that the first HPLC peak contained the 191 residue alpha(s1)-casein mo lecular species and the second the 199 residue species, in proportions of similar to 20:80. Only in the case of the sample containing alpha( s1)-casein CE was the method for the separation of the single short an d long forms of each variant unsuccessful. Both two dimensional electr ophoresis followed by staining with polyclonal antibodies against alph a(s1)-casein and electrospray mass spectrometry showed a heterogeneity consistent with that expected from a protein chain with three levels of phosphorylation and two different lengths. However, especially for alpha(s1)-caseins D and E, a further uncharacterized heterogeneity was detected.