Binding of serum amyloid P component to heparin in human serum

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Abstract

It has been proposed that the function of serum amyloid P component (SAP) may closely relate with its binding to polysaccharides, especially glycosaminoglycans. We employed a quantitative immunoelectrophoresis (QIE) method and a native polyacrylamide gel electrophoresis (PAGE) method to characterize the SAP-heparin binding in soluble state. The SAP-heparin binding showed positive cooperativity. The apparent numbers of heparin molecules bound to SAP varied with the calcium concentration with a ratio of 1:1 (SAP/heparin), a Kd of 2.06·10−7 M at 0.1 mM CaCl2 and a ratio of 1:1.6 (SAP/heparin), a Kd of 3.91·10−7 M at 2 mM CaCl2, when estimated by the QIE method. No binding between SAP and heparin was observed in the absence of calcium. Magnesium and barium failed 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 regular to modulate the anticoagulant activity of SAP and a useful drug to prevent SAP deposition on amyloid deposits.

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    1

    Visiting scholar from Taishan Medical College, Taian, Shandong, China, financially supported by the Japan Health Science Foundation.

    2

    Visiting scholar from Taian Central Hospital, Taian, Shandong, China.

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