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

Abstract

SummaryWhen whole caseins from cow and Italian buffalo (Bubalus arnee) were fractionated by chromatography on a column of hydroxyapatite they behaved in a similar manner. κ-Casein was eluted with 5 mM phosphate buffer, pH 6·8, containing 0·2 M-KCI, 4·5 M-urea and 2 mM-2-mercaptoethanol, but β- and αs-caseins were retained and could be eluted successively by a linear gradient from 5 mM to 250 mMphosphate buffer. Buffalo κ-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 κ-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 κ-casein B.