Micelle formation in beta-casein solutions

We have studied by Small Angle Neutron Scattering the structure of beta-casein in aqueous solutions in a wide range of temperatures and denaturant concentrations. For higher temperatures and low denaturant concentrations, we find micelles. These may be described by using a two shell model with constant concentration in every shell. When either temperature is lowered or denaturant concentration is raised, the aggregation number of the micelles decreases, until it reaches unity at a critical temperature or a critical concentration. Beyond this threshold, single isolated casein molecules are present. For both cases, the results are interpreted in terms of synthetic polymers, by a copolymer model. We introduce an excluded volume parameter describing the hydrophobic sequences. We assume that it depends on both temperature and denaturant concentration, that varies and eventually changes sign as either of these parameters is varied. This leads to some power law variations that are in reasonable agreement with the experiments.