Subunit structure of casein micelles from small-angle neutron-scattering

Wet pellets of whole casein micelles of cows' milk have been studied by small-angle neutron-scattering. Contrast variation using 2H2O/H2O mixtures showed that the previously observed inflection in scattered intensity at Q[4 pi sin theta)/gamma) = 0.035 A-1 is due primarily to scattering from protein, and not from calcium phosphate. Agreement between measured scattering and that calculated for a simple model of packed protein subunits suggests that the whole micelle contains protein subunits of the approximate size of free casein submicelles, packed in a short-range ordered arrangement.