A preliminary study by gel filtration and ultracentrifugation of the interaction of bovine milk caseins with detergents

Abstract

Summary: The detergents sodium dodecyl sulphate and octyl phenoxy polyethoxyethanol interact with casein and cause dissociation of the high-molecular-weight casein aggregates. It is presumed that the detergent binds with hydrophobic regions in the casein molecule. The size of the complexes formed between detergents and α_s1-casein, β-casein and κ-casein, as estimated by gel filtration and sedimentation velocity experiments, suggests that the caseins were complexed as monomers.During gel filtration under non-reducing conditions, detergent-κ-casein complexes were separated from other major components because of their conversion through formation of disulphide bonds into high-molecular-weight aggregates. This reaction, which did not occur in sedimentation velocity experiments, was presumably facilitated by the changes in the equilibrium between the individual caseins during gel filtration.Sedimentation velocity experiments showed that a ratio of about 40 detergent molecules to 1 casein molecule was required to give the smallest casein-detergent complex.