title: A thermodynamic model for the self-association of human spectrin.
abstract: The self-association of human spectrin at 28.8 degrees C in 0.11 M salt (pH 7.5) has been studied by means of sedimentation equilibrium. Coincidence of omega function plots as a function of total spectrin concentration (0-2 g/L) indicated that equilibrium was achieved and that no significant concentration of solute was incapable of participating in the self-association reaction. On the basis of the root-mean-square deviation of the fits and the randomness of the residuals, the behavior can be described equally well, either by a cooperative isodesmic model, in which K12 approximately 2 x 10(6) M-1 and all other K approximately 10(6) M-1, or by an attenuated scheme in which K(i-1)i approximately (3.5 x 10(6)/i M-1. The returned values of the second virial coefficient, B, for both these models fall within the range calculated from the charge and Stokes radius of spectrin. A mechanism for spectrin self-association consistent with both schemes is proposed in which spectrin heterodimers undergo a reversible opening at the self-association interface. These open heterodimers then undergo indefinite self-association to form a series of open-chain oligomers in dynamic equilibrium with closed-loop oligomers.
authors.affiliation: Department of Biochemistry, University of Sydney, NSW, Australia.
authors.forename: M
authors.initials: M
authors.lastname: Morris
authors.forename: G B
authors.initials: GB
authors.lastname: Ralston
mesh_terms: D055598:Chemical Phenomena; D002627:Chemistry, Physical; D006801:Humans; D046911:Macromolecular Substances; D008433:Mathematics; D008954:Models, Biological; D013049:Spectrin; D013816:Thermodynamics
chemical_list: D046911:Macromolecular Substances; D013049:Spectrin