Formation of the poly(Lys-Ala-Ala) complex with pectin of various esterification degree

The helix-forming interaction of poly(Lys-Ala-Ala) with potassium pectinates of various esterification degree (E 0-87%) was quantitatively investigated by circular dichroism spectra. The helix-forming effect of pectinates is significant even at a low density of carboxyl anions in the molecule at a high esterification degree. The mutual complementarity of linear charge density of both interacting polyions plays a decisive role. The charge densities of unesterified pectate and helical poly(Lys-Ala-Ala) are very close. Orientation of the potassium pectate macromolecule (E0%) in the proposed spatial model is parallel to the axis of poly(Lys-Ala-Ala) α-helix. Saturation of the polypeptide charge with pectinates of an esterification degree E > 0% is achieved through formation of a superhelical structure of the pectinate with a turn density corresponding to the equivalence of charge densities of both interacting components in the complex.