Casein electrophoretic pattern

Peptides extracted from casein with N, N-dimethyl formamide have complex electrophoretic patterns identical to those of the fraction first prepared by Long and co-workers and called X-casein (El-Negoumy 1973). These peptides are identical electrophoretically to those released by the action of plasmin, which is present in fresh raw milk, upon asr casein (Aimutis and Eigel 1982). Two of these peptides have tryptic peptide maps and molecular weights identical to those of a pair of the peptides produced by plasmin degradation of asl-casein. These peptides appear to be fragments of a8l-casein which are present in milk as the result of plasmin proteolysis. More definitive information on their primary structure is needed before nomenclature for these fragments can be established. 

Fig. 4. Electrophoretic patterns of unfractionated casein, a-casein, and 8-casein (taken from Perlmann (69)).

Fiu. 5. Tracings of electrophoretic patterns of a-casein hefore and after treatment with prostate phosphatase (taken from Perlmann (60)). 

The progress of proteolysis can be followed by electrophoretic and chromatographic methods, e. g., via the peptide pattern obtained with the help of RP-HPLC (Fig. 10.29) and via changes in concentration of individual peptides which correspond to certain casein sequences (Table 10.33) and can serve as an indicator of the degree of cheese ripening. 

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