Albumin Aggregates: Hydrodynamic Shape and Physico-Chemical Properties

Although albumin was known for more than a century, little is known about its tertiary structure. At present two models are known to represent its molecular conformation: the heart- shaped and the prolate ellipsoid. Our results support the prolate ellipsoid model for albumin in slightly alkaline solution. Albumin in solution exists as a monomer and higher aggregates. We isolated the monomer, dimer, tetramer, and hexamer of bovine serum albumin by gradient polyacrylamide gel electrophoresis followed by electroelution. The monomer was stable for 5 months at 8oC, whereas the dimer and tetramer dissociated into smaller forms within few hours after their separation but no higher aggregates were detected. Albumin forms are surrounded by about three layers of water, with Stokes’ radii of 3.55, 4.34, 5.18, and 5.85 nm for monomer, dimer, tetramer, and hexamer, respectively. The effective negative charge and density of surface charge (- esu.cm-2), respectively, were 14 and 4244 (monomer), 12.3 and 2495 (dimer), and 10.2 and 1452 (tetramer). The translational diffusion coefficients were 5.88, 4.81, 4.03, and 3.57 cm2.s-1 for monomer, dimer, tetramer, and hexamer, respectively. Other physico-chemical properties were calculated such as: frictional coefficient, sedimentation coefficient, electrophoretic mobility, volume of hydrated and unhydrated molecules.