QUANTITATIVE ASSESSMENT OF THE ASSOCIATION OF THE ALPHA-I FRAGMENT OFSPECTRIN WITH OLIGOMERS OF INTACT SPECTRIN

1. The alpha-I fragment of human spectrin that carries the binding sit e on the alpha-chain of spectrin for the beta-chain has been purified from limited trypsin digests of spectrin by means of FPLC. 2. The self -association of spectrin and the binding of the alpha-I fragment to sp ectrin heterodimers and to tetramers have been quantified through the use of gel electrophoresis, staining with Coomassie Blue, and quantifi cation of the bound dye following elution with pyridine. 3. The parame ters of self-association were found to be consistent with those estima ted from sedimentation equilibrium analysis. 4. The data were consiste nt with a model in which both self-association and the binding of the alpha-I fragment are considered to occur through an intermediate in wh ich the alpha-beta interface is initially dissociated. The alpha-beta interface in the heterodimer was found to be less stable than that of higher oligomers by approx. 3 kJ/mol.