Purification of disulphide-linked αs2- and κ-casein from bovine milk

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Abstract
Summary: Naturally occurring disulphide-linked αs2- and κ-casein in bovine milk were purified by gel chromatography on a column of Sepharose CL-6B. Four fractions (A–D) were obtained by elution with ammonium acetate-urea buffer. Fractions A and B, identified by SDS gel electrophoresis and amino acid sequence analysis, corresponded to disulphide-linked κ-casein and αs2-casein respectively. Fraction C consisted of a mixture of αs1-, αS2-, and β-casein. Separation of fraction C into its components was achieved by reversed-phase HPLC. The stability of the disulphide bridges in αs2- and κ-casein was shown to differ with respect to reducing agents (dithioerythritol and 2-mercaptoethanol).