Colloidal properties of human transferrin receptor in detergent free solution

The colloidal properties of transferrin receptor, isolated from human place nta, in detergent free solution has been investigated by light scattering t echniques and analytical ultracentrifugation. In detergent free solution at 293.2 K, hTfR forms stable aggregates with an apparent hydrodynamic radius of 17 nm. The molecular mass was determined by ultracentrifugation to lie between (1722 +/- 87) kDa (sedimentation equilibrium) and (1675 +/- 46) kDa (sedimentation velocity). This implies that the aggregates are build up fr om nine hTfR dimers. Based on model calculations, which are in good agreeme nt with the experimental data, we propose a torus-like structure for the ag gregates. Upon pH shift from pH 7.5 to 5.0 or removal of the N-linked carbo hydrate chains, formation of larger aggregates is induced. These aggregates can be described in terms of porous fractal structures. We propose a simpl e model, which accounts for that behaviour assuming that the aggregation is mainly due to the reduction of negative surface charge. (C) 2000 Elsevier Science B.V. All rights reserved.