a1 Dipartimento di Scienza degli Alimenti, Universitá degli Studi di Napoli Federico II, Parco Gussone, 1-80055 Portici, Italia
a2 Istituto Sperimentale Lattiero-Caseario, Via A. Lombardo 11, 1-20075 Lodi, Italia
Five ovine αsl-casein variants (A–E) were identified in an Italian population sample using gel electrophoresis at alkaline pH, gel isoelectric focusing, two dimensional gel electrophoresis, and immunoblotting with polyclonal antibodies against αs1-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 αsl-casein molecular species and the second the 199 residue species, in proportions of 20:80. Only in the case of the sample containing αsl-casein CE was the method for the separation of the single short and long forms of each variant unsuccessful. Both two dimensional electrophoresis followed by staining with polyclonal antibodies against αsl-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 αsl-caseins D and E, a further uncharacterized heterogeneity was detected.
(Received July 18 1994)
(Accepted May 16 1995)