PARTICLE SIZES OF PURIFIED KAPPA-CASEIN - METAL EFFECT AND CORRESPONDENCE WITH PREDICTED 3-DIMENSIONAL MOLECULAR-MODELS

kappa-Casein as purified from bovine milk exhibits a rather unique dis ulfide bonding pattern as revealed by SDS-PAGE. The disulfide-bonded c aseins present range from dimer to octamer and above and preparations contain about 10% monomer. All of these heterogenous polymers, however , self-associated into nearly spherical uniform particles with an aver age radius of 8.9 nm as revealed by negatively stained transmission el ectron micrographs. Evidence is presented that multivalent cations pla y a role in the stabilization of these spherical particles. Treatment with EDTA causes disruption of the kappa-casein particles and leads to a broader size distribution as judged by electron microscopy and dyna mic light scattering. The size and shape of the particles are in accor d with earlier proposed 3D models for kappa-casein that actually predi cted participation of divalent cations in the structure.