Structural Studies on Bovine Casein Micelles by Laser Light Scattering
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,Pi and citrate, but the principal salt constituents are Ca and Pi 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.
KeywordsCalcium Phosphate Casein Micelle Laser Light Scattering Weight Average Molecular Weight Colloidal Dimension
Unable to display preview. Download preview PDF.
- 2.C. Holt, S. S. Hasnain and D. W. L. Hukins, Structure of bovine milk calcium phosphate determined by x-ray absorption spectroscopy, Biochim. Biophys. Acta (in the press).Google Scholar
- 3.C. Holt, D. G. Dalgleish and R. Jenness, Calculation of the ion equilibria in milk diffusate and comparison with experiment, Anal. Biochem. 113: 154 (1981).Google Scholar