ASSOCIATION STATE, OVERALL STRUCTURE, AND SURFACE-ROUGHNESS OF NATIVE OVALBUMIN MOLECULES IN AQUEOUS-SOLUTIONS AT VARIOUS IONIC CONCENTRATIONS

The shape, size, and surface roughness of a globular molecule of ovalbumin (OA) were studied with small angle X-ray scattering over a wide concentration range from 0 to 300 mM of phosphate buffer solution. The Guinier approximation can be sufficiently applied over a relatively wide range of the small scattering angle. The radius of gyration of the native OA molecule can be obtained as ca. 27 Å and it is almost independent of the concentration of the buffer solution. The native OA molecule is spherical and the radius of the molecule is ca. 25 Å over the concentration range from 0 to 300 mM of buffer solution. The specific inner surface, Os, of the native OA molecule, which is obtained at low and high OA concentrations at various buffer concentrations, is approximately 1.8 times that of a sphere with a smooth surface. The value of Os is almost independent of the concentration of the buffer solution. The surface roughness of the OA molecule is also discussed in comparison with that of the micelles and vesicle. © 1993 Academic Press, Inc.