Environmental influences on the particle sizes of purified kappa-casein: metal effect

Kappa-casein as purified from bovine milk exhibits a rather unique disulfid e bonding pattern as revealed by SDS-PAGE. The disulfide bonded caseins pre sent, range from dimer to octamer and above and preparations contain about 10% monomer. All of these heterogeneous polymers, however, self-associate i nto nearly spherical uniform particles with an average radius of 8.9 nm as revealed by negatively stained transmission electron micrographs. Evidence is presented that multivalent cations play a role in the stabilization of t hese spherical particles. Treatment with EDTA causes disruption of the kapp a-casein particles and leads to a broader size distribution as judged by el ectron microscopy, dynamic light scattering and analytical ultracentrifugat ion. The size and shape of the particles are in accord with earlier propose d 3D models for kappa-casein, that actually predicted participation of diva lent cations in the structure. Published by Elsevier Science Ltd.