Preparation of red-cell-membrane cytoskeletal constituents and characterisation of protein 4.1.

A new and rapid method is described for the preparation of protein 4.1, the protein which modulates the interaction between spectrin and actin in the membrane cytoskeleton of the red cell. The method is based on the dissociation of purified membrane cytoskeletons in concentrated Tris at neutral pH, followed by gel filtration in the same medium. This procedure also yields spectrin and actin, as well as the fourth cytoskeletal constituent, protein 4.9, in relatively pure form, and ankyrin. Protein 4.1 is monomeric under our conditions of solvent and protein concentration, with a relative molecular mass, as determined from sedimentation equilibrium, of about 78 000; its sedimentation coefficient and Stokes' radius are those of a globular, though somewhat asymmetric or flexible molecule. It forms a strong complex with F-actin and spectrin. Protein 4.9 is also recovered in active form, and will bind strongly to F-actin.