Small-angle neutron scattering study of bovine casein micelles and sub-micelles

Whole micelles and sub-micelles of cows' milk casein have been studied in solution by small-angle neutron scattering. Sub-micelles were found to have a mean molecular weight of approximately 3.0 × 10⁵ and a radius of gyration (R_g) in ²H₂O of 65 Å. R_g² appeared to decrease slightly with increasing reciprocal contrast (1/-?) whereas most globular proteins show the opposite behaviour. Estimated voluminosity (hydrated specific volume) of sub-micelles was 4.0 to 5.5 ml/g, which is much higher than values from electron microscopic measurements on whole micelles.Scattering from whole micelles showed an inflection at $\text{Q((}\text{4π sin θ)}\text{λ}\text{) = 0.035}\text{A}\text{?}{}^{\mathrm{?1}}$), which was attributed to inter-sub-micelle interference within the whole micelle.