Complex formation in the ternary system of amylose (degree of polymerization, DP, 1100), SDS, and iodine was studied statically by spectrophotometry and amperometric titration and kinetically by the pressure-jump method. It was clarified that (1) iodine (Is) to some extent binds to amylose saturated with SDS to form an inclusion complex (AS1 system); (2) the binding of SDS apparently transforms amylose of DP 1100 to that of much lower DP (less than 60) from the viewpoint of iodine binding; and (3) iodine binds to sites unoccupied by SDS in the center of the helical segment of amylose.
Pressure-jump relaxation phenomenon was not observed in solutions in which iodine was dissolved prior to SDS (AIS system), but it was observed in the AS1 system; it is ascribed to the association and dissociation of three molecules of iodine in the center of the amylose helix. Comparison of the rate constants in the AS1 system with those in the amylose (DP 32) and iodine system indicates that iodine runs to and from the helical segment of amylose perpendicularly to the axial plane in the former, while it runs horizontally in the latter. We discuss the order of ligand mixing on the resulting structure of the ternary complexes of amylose, SDS, and iodine.