Molecular Weights of Three Mouse Milk Caseins by Sodium Dodecyl Sulfate-Polyacrylamide Gel Electrophoresis and κ-Like Characteristics of a Fourth Casein

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Abstract
Caseins of mouse milk are phosphoproteins which precipitate at pH 4.6, stain blue with Stains-all, and stain red with Stains-all following alkaline phosphatase digestion. Four caseins were separated electrophoretically in sodium dodecyl sulfate-polyacrylamide gels varying from 8.5-15% acrylamide. MW for 3 of these proteins were 43,200, 27,700 and 25,900. The molecular weights determined for bovine .alpha.s1 and .beta. caseins by this method were similar to those previously obtained by other methods. A 4th mouse casein contained carbohydrate, P and sialic acid. This protein was renin-sensitive and behaved anomalously on sodium dodecyl sulfate polyacrylamide gels, as did bovine .kappa.-casein. Because of similarities with bovine .kappa.-casein, it was designated the .kappa.-casein of mouse milk.