Direct potentiometric membrane electrode measurements of heparin binding to macromolecules

The use of a newly developed heparin responsive polymeric membrane electrode for directly monitoring the binding of heparin to a variety of other biological macromolecules is examined. Potentiometric titrations of protamine, low‐density lipoprotein (LDL), polybrene, DNase enzyme, and polylysine with either porcine or beef lung heparin can be followed conveniently by the electrode at various solution pHs. Such titrations yield endpoints that are used to determine the stoichiometry for the interaction of the different heparins with these macromolecules. Based on prior heparin calibration curves, the titration data can be recast in Scatchard form to obtain binding constants for these solution‐phase heparin‐macromolecular reactions. The speed and simplicity of the proposed method make it an attractive alternative to classical solid‐phase binding methods or newer homogeneous fluorescent polarization schemes for studying the solution‐phase interaction of heparin with other macromolecules.