Fractionation of whole casein on hydroxyapatite. Application to a study of buffalo kappa-casein.

When whole caseins from cow and Italian buffalo (Bubalus arnee) were fractionated by chromatography on a column of hydroxyapatite they behaved in a similar manner. kappa-Casein was eluted with 5 mM phosphate buffer, pH 6-8, containing 0-2 M-KCl, 4-5 M-urea and 2 mM-2-mercaptoethanol, but beta- and alphas-caseins were retained and could be eluted successively by a linear gradient from 5 mM to 250 mM-phosphate buffer. Buffalo kappa-casein preparations, obtained from bulk milk or from milks of individual animals by chromatography on hydroxyapatite, produced identical electrophoretic patterns at pH 8-6. By further fractionation of these kappa-caseins on DEAE-cellulose, in each case, at least 7 components were purified; they had different electrophoretic mobilities but were all sensitive towards chymosin. The major fraction migrated like component 1 of bovine kappa-casein B.