Molecular Weights of Fractionated Bovine Milk Casein Micelles from Analytical Ultracentrifugation and Diffusion Measurements

Abstract

Native skimmilk casein micelles were fractionated into relatively monodisperse size fractions and examined by analytical ultracentrifugation. Sedimentation patterns confirmed the monodispersity of the micelle fractions previously observed by electron microscopy, resedimentation by rate-zone ultracentrifugation, and inelastic light scattering. Sedimentation coefficients (S20, W) for two micelle fractions were 800 and 2200 S. Diffusion coefficients (D20, W) for these two fractions, measured by inelastic light scattering, were 2.82×10−8cm2/sec and .97×10−8cm2/sec. Application of the Svedberg equation led to molecular weights of these two micelle fractions of 2.3×108 and 1.8×109.