Structural Studies on Bovine Casein Micelles by Laser Light Scattering

Abstract

Bovine casein micelles are more-or-less spherical particles of colloidal dimensions, composed of 4 phosphoprotein types. The weight average molecular weight is about 5 × 10⁸ and average radii by light scattering methods are generally 80–150nm, although there is a broad range of sizes¹. Besides the phosphoproteins, casein micelles contain Ca, Mg,P_i and citrate, but the principal salt constituents are Ca and P_i in the form of a calcium phosphate salt and calcium bound directly to sites on the casein. It appears that the phosphate groups of the phosphoproteins are largely incorporated in the lattice of the calcium phosphate² and hence that the calcium phosphate could be responsible, in part, for holding together casein micelles. On the other hand, caseins can associate in the presence of mM concentrations of Ca²⁺ to give aggregates of the same size as natural casein micelles. In many physico-chemical studies this has been assumed to be the mechanism of formation of micelles and the possible role of calcium phosphate has been neglected.