BINDING OF SERUM AMYLOID-P COMPONENT TO HEPARIN IN HUMAN SERUM

It has been proposed that the function of serum amyloid P component (S AP) may closely relate with its binding to polysaccharides, especially glycosaminoglycans. We employed a quantitative immunoelectrophoresis (QIE) method and a native polyacrylamide gel electrophoresis (PAGE) me thod to characterize the SAP-heparin binding in soluble state. The SAP -heparin binding showed positive cooperativity. The apparent numbers o f heparin molecules bound to SAP varied with the calcium concentration with a ratio of 1:1 (SAP/heparin), a K-d of 2.06.10(-7) M at 0.1 mM C aCl2 and a ratio of 1:1.6 (SAP/heparin), a K-d of 3.91.10(-7) M at 2 m M CaCl2 when estimated by the QIE method. No binding between SAP and h eparin was observed in the absence of calcium. Magnesium and barium fa iled to induce the formation of SAP-heparin complex. Furthermore, they showed inhibitory effects on the calcium-mediated complex formation. We propose that heparin might be a regulator to modulate the anticoagu lant activity of SAP and a useful drug to prevent SAP deposition on am yloid deposits.