Heparin-like activity of insoluble sulfonated polystyrene resins: II. Properties of polyampholytes

Abstract

Insoluble sulfonated polystyrene resins are endowed with heparin-like activity toward coagulation of blood plasma induced by thrombin (catalysis of the neutralization of thrombin by antithrombin). By introducing variable amounts of amino groups and sulfonate groups on the same chains of polystyrene resins (Polyampholytes = PA), the effects of the net charge borne by the PA resins on the binding of hydrogen ions, heparin-like properties and the adsorption of thrombin were studied. It was demonstrated that the apparent acidity constant of the amino groups was strongly dependent upon the electrical environment of these groups: they behaved like strong bases when surrounded by negative charges and like weak bases when surrounded by positive charges. This behavior was in agreement with the theory of Katchalsky concerning PA. This model was used to explain why the affinity of thrombin for sulfonate groups strongly decreased when these groups were surrounded by positively charged amino groups. The adsorption of active thrombin was strongly involved in the heparin-like properties of the hydrophilic resins bearing a net negative charge. In the presence of the hydrophobic resins bearing a net positive charge, no adsorption of active thrombin was detected. The gross effect of one positively charged amino group was to neutralize the heparin-like activity of one sulfonate group.