Cu(2+)-heparin interaction studied by polarimetry.

Plots analogous to isothermal binding curves were derived from polarimetric studies of solutions of Na(+)-heparin to which Cu2+ was added. The shape of the plots suggests that discrete Cu(2+)-heparin complexes may form, the nature and stoichiometry of which depend upon the conditions under which the interaction occurs. Initially, complexes were formed with a stoichiometry of about 1 Cu2+ ion per heparin tetrasaccharide unit. Under these conditions, the complex may exist as a colloid-like phase that is not subject to simple solution equilibrium processes, and that is maintained by forces in addition to electrostatic ones. Further addition of Cu2+ resulted in the formation of a different complex with a stoichiometry of about 1 Cu2+ ion per disaccharide unit.