SMALL-ANGLE X-RAY-SCATTERING AND VISCOELASTIC STUDIES OF THE MOLECULAR SHAPE AND COLLOIDAL STRUCTURE OF BOVINE AND RAT SERUM ALBUMINS IN AQUEOUS SYSTEMS

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 theological measurements. The BSA and RSA molecules disperse in a state of association number of approximate to 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 approximate to 68 and 19 Angstrom. The volume of the BSA and RSA molecules is approximate to 1.0 x 10(5) Angstrom(3). The serum albumin colloidal systems show a remarkable yield stress sigma(y) and a rigidity G due to some solid-like structure which is mainly detected by the theological methods even in very dilute systems such as 0.01 wt%. The values of sigma(y),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 approximate to 0.03 to 10 wt%. In spite of the fact that this theological behaviour is very characteristic, it seems to be a common property of the various albumin systems.