Immunological Approach to Location of κ-Casein in the Casein Micelle by Electron Microscopy

The colloidal stability of skim milk is due to K-casein in casein micelles; thus, the location of this protein within these complexes has been the subject of speculation. Various models have placed Kcasein at the surface, in the interior, or distributed uniformly in the casein micelle. By a ferritin-labeled doubleantibody technique coupled with electron microscopy, location of K-casein has been related to casein micelle size. Casein micelles with K-casein located predominantly at the periphery of the micelle have diameters of 1420 +-320 )k whereas micelles with K-casein located uniformly throughout have diameters of 920 -+ 220 ~.. These results are in accord with the inverse relationship between micelle size and K-casein content and support the model of Slattery (19).