Binding isotherms and kinetics of interaction for α-spectrin fragments to spectrin in intact membranes. (A and B) Binding of α-spectrin fragments to membranes. Open squares, αI; solid squares, αII; open circles, αIIαI; solid circles, αIαII. The curves are calculated, assuming a set of independent identical sites in each case. B shows the data plotted on a log scale. (C) Association rates for αI (open squares), αII (filled circles), αIαII (filled squares), and αIIαI (open circles) peptides; (D) dissociation rates of αI (open circles) and αII (closed circles) peptides from membranes. The curve is calculated from the initial rate (see text).