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

Summary The specificity of the interaction betweenκ-casein,αs-casein andβ-casein which forms the basis of micelle stabilization was studied by investigating the extent to whichκ-casein could be replaced by other proteins. Of those tested, only gelatin replacedκ-casein and even it was only 2·5% (w/v) as effective and required a long pre-incubation period. The micelles formed by each ofκ-casein and gelatin withαs-casein and Ca2+were of a similar size to the casein—Ca complexes which compose natural micelles. Gelatin also formed complexes withαs- and withβ-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 betweenκ-casein and the other caseins. It was concluded that the interactions betweenκ-casein andαs- andβ-caseins which lead to micelle formation are highly specific and probably involve definite sites in each molecule.