title: The effects of ionic strength on the self-association of human spectrin.
abstract: The self-association of human spectrin has been studied by means of sedimentation equilibrium in the analytical ultracentrifuge at pH 7.5 and over a range of ionic strength from 0.009 to 1.0 M. Increasing ionic strength above 0.1 M reduces the equilibrium constants for all of the measurable steps in the self-association reaction. These results support the concept of charge-charge interactions stabilizing the tetramer and higher oligomers with respect to the heterodimer. In addition, increasing ionic strength brought about a dissociation of the heterodimer to component polypeptide chains. Dissociation to the heterodimers is also enhanced with a decrease in ionic strength below 0.05 M. This low ionic strength-dependent dissociation is consistent with generalised electrostatic repulsion; however, this effect also correlates with some loss of alpha-helical content as revealed by circular dichroism. The secondary, tertiary and quaternary structures may all be partially disrupted by electrostatic free energy at low ionic strength.
authors.affiliation: Department of Biochemistry, University of Sydney, Australia.
authors.forename: N
authors.initials: N
authors.lastname: Cole
authors.forename: G B
authors.initials: GB
authors.lastname: Ralston
mesh_terms: D004910:Erythrocyte Membrane / Q000378:metabolism; D006801:Humans; D007700:Kinetics; D046911:Macromolecular Substances; D008433:Mathematics; D008962:Models, Theoretical; D009994:Osmolar Concentration; D013049:Spectrin / Q000737:chemistry* / Q000302:isolation & purification; D014461:Ultracentrifugation / Q000379:methods
chemical_list: D046911:Macromolecular Substances; D013049:Spectrin