A reappraisal of the self-association of human spectrin.

The self-association behaviour of human spectrin has been re-examined through a study of sedimentation equilibrium, sedimentation velocity and gel electrophoresis. In all cases we find evidence for oligomers of spectrin larger than the tetramer, even at low concentration. The data are not consistent with a simple dimer-tetramer model, but instead indicate an open, or indefinite, pattern of association. Although a good fit to the data can be achieved with the isodesmic reaction model, with an equilibrium constant in agreement with the value previously determined for the dimer-tetramer reaction, there is other evidence suggesting that the actual association scheme may be somewhat more complex.