Small angle X-ray scattering and viscoelastic studies of the molecular shape and colloidal structure of bovine and rat serum albumins in aqueous systems

Abstract

The shape and the colloidal structure of bovine serum albumin (BSA) and rat serum albumin (RSA) molecules in sodium phosphate buffer solution have been studied using light scattering, small angle X-ray scattering and rheological measurements. The BSA and RSA molecules disperse in a state of association number of ≈ 1.8 and ≈ 1.3, respectively, over the concentration range from 0.02 to 1 wt%. The shape of the BSA molecule is assumed to be a prolate ellipsoid with semi-axes of ≈ 68 and 19 Å. The volume of the BSA and RSA molecules is ≈ 1.0 × 105 Å3. The serum albumin colloidal systems show a remarkable yield stress σy and a rigidity G due to some solid-like structure which is mainly detected by the rheological methods even in very dilute systems such as 0.01 wt%. The values of σy and G, approximately 0.1 Pa for the BSA and 0.08 Pa for the RSA system, remain almost constant over a wide concentration range from ≈ 0.03 to 10 wt%. In spite of the fact that this rheological behaviour is very characteristic, it seems to be a common property of the various albumin systems.