The influence of temperature and electrolytes upon the apparent size and shape of α- and β-casein

Abstract

Viscosity measurements in Veronal buffer and sedimentation analyses either in Veronal or phosphate buffer have demonstrated the marked tendency of β-casein to form aggregates at room temperature. The molecular weight of this protein as determined from sedimentation and diffusion analyses conducted below 15 °C. was 24,100. These measurements were in agreement with viscosity measurements at reduced temperatures in showing that β-casein is a rod-shaped molecule. Although numerous measurements have indicated that whole casein is a complex formed from rather small molecules, the apparent molecular weight of α-casein in Veronal buffer was 121,800 as calculated from sedimentation and diffusion analyses. The diffusion patterns suggested some heterogeneity, and marked disagreement was noted between the axial ratios calculated from these analyses and those obtained from viscosity measurements. Viscosity measurements, light-scattering studies, and sedimentation analyses in phosphate buffer produced evidence that the aggregation of α-casein is dependent upon ionic strength rather than temperature.