The specificity for κ-casein as the stabilizer of αs-casein and β-casein. I. Replacement of κ-casein by other proteins

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Abstract
The specificity of the interaction between κ-casein, αs-casein and β-casein which forms the basis of micelle stabilization was studied by investigating the extent to which κ-casein could be replaced by other proteins. Of those tested, only gelatin replaced κ-casein and even it was only 2·5% (w/v) as effective and required a long pre-incubation period. The micelles formed by each of κ-casein and gelatin with αs-casein and Ca2+ were of a similar size to the casein—Ca complexes which compose natural micelles. Gelatin also formed complexes with αs- and with β-casein at 30°C in the absence of CaCl2. Evidence was obtained that the interactions between gelatin and the caseins had a much stronger ionic component than had those between κ-casein and the other caseins. It was concluded that the interactions between κ-casein and αs- and β-caseins which lead to micelle formation are highly specific and probably involve definite sites in each molecule.