REINVESTIGATION OF THE THERMODYNAMICS OF SPECTRIN SELF-ASSOCIATION

The thermodynamics of the self-association reactions of human spectrin have been reinvestigated by means of sedimentation equilibrium over t he temperature range 18-40 degrees C. The experimental data were analy sed in terms of a cooperative isodesmic model of association. The van' t Hoff plot showed that the standard change in enthalpy for the hetero dimer-tetramer step was temperature-dependent, leading to an estimate of -8.5 kJ mol(-1) K-1 for the change in molar heat capacity, Delta C- p. Curvature in the van't Hoff plots, not detected in previous studies , was revealed through the increased precision of the data and the wid er temperature range examined. On the assumption that Delta C-p reflec ts hydrophobic interactions in the tetramer that cannot be formed in t he heterodimer, it can be estimated that approximately 50 CH2 groups p er heterodimer participate in hydrophobic interactions in the tetramer that cannot be formed in the heterodimer.