Interaction of Amylose with Iodine. I. Characterization of Cooperative Binding Isotherms for Amyloses

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Abstract
The interaction of amylose with iodine was investigated as a function of degree of polymerization (DP) of amylose by amperometric titration, and the binding isotherms were obtained. The intrinsic equilibrium constant and cooperative parameter were determined with a one-dimensional Ising model for amyloses of various DPs. The inflection of the plot of the intrinsic equilibrium constant vs. DP observed at about DP 60 suggests that a helical segment of amylose consists of anhydroglucose residues less than 60. The discontinuity of the cooperativity at about DP 60 was interpreted by two kinds of cooperative effects, intra- and interhelical effects. These results suggest that the interrupted helix is a good model for the amylose structure in aqueous solution. The temperature dependencies of the cooperative parameters show that the cooperativity of amylose-iodine complexation is entropycontrolled.