STRUCTURE OF CASEIN MICELLES .1. SMALL-ANGLE NEUTRON-SCATTERING AND LIGHT-SCATTERING FROM BETA-CASEIN AND KAPPA-CASEIN

Casein is the main protein component of milk and is of remarkable colloidal stability. Under the influence of milk clotting enzymes casein shows the striking behavior of coagulation. This clotting process has already been studied by other groups, neglecting the fact that casein is not a homogeneous protein. The purpose of the present study is focused, in this first stage, on the determination of the structure of the various casein components. In cooperation with other laboratories we have been able to obtain the well separated individual proteins. Studies have been performed so far with beta - and chi -casein. For detailed structural information we carried out small angle neutron scattering and combined static and dynamic light scattering measurements and determined the molecular weight, the radius of gyration, the hydrodynamic radius, the Q-value and the particle scattering factor. The two caseins show a strikingly different behavior. For the beta -casein we found a star-like structure, i. e. an aggregation pattern that is expected for a common micelle. The micelle consists of about 38 monomer chains. The aggregates of chi -casein appear to be composed of star-like submicelles, where each submicelle contains nine chi -casein chains and the total degree of aggregation is about 140.