Examination of the discrepancy between size estimates for ovalbumin from small-angle X-ray scattering and other...

Examination of the solution behavior of ovalbumin by small-angle X-ray scattering, dynamic light scattering, and analytical ultracentrifugation methods confirms its existence as a 44-kDa monomer in 20 mM phosphate, pH 7.0, thereby contradicting the discord introduced by published SAXS studies in favor of a dimeric state for this protein at neutral pH. Although the theoretical interpretation of SAXS measurements considers the consequences of thermodynamic nonideality arising from the repulsive interactions between molecules only if they give rise to a positive second virial coefficient, the fact that A(2) is negative for the present system does not account for the earlier findings.