Hydrodynamic characterization of the heterodimer of spectrin

The hydrodynamic properties of the spectrin dimer have been examined. The S20,w value of 9.3 S and the D20,w value of 1.75 x 10(-7) cm2 x s-1 yield a molecular weight of 470 000, in good agreement with the value from sedimentation equilibrium of 460 000. The frictional ratio of 2.3 and the intrinsic viscosity of 36 ml/g are not consistent with a compact, globular structure, but the value of the parameter Ks/[eta], 1.15, is not consistent with a rigid rod model. The most appropriate model, consistent also with data from other laboratories, is of a flexible, kinked rod-like molecule.