Binding reactivity of C-reactive protein for polycations. II. Modulatory effects of calcium and phosphocholine.

C-reactive protein previously was shown to selectively and reversibly precipitate with certain small polymers of arginine and lysine. In the present report, calcium was shown to inhibit this reactivity in a dose-dependent manner, in direct contrast to the requirement for calcium for precipitation of CRP with C-polysaccharide. However, in the presence of phosphocholine, CRP rapidly precipitated and formed stable complexes with the polycationic polymers in the otherwise inhibitory calcium concentrations. alpha-Glycerol-phosphocholine, unlike phosphocholine, did not reverse this inhibitory effect. These results extend the characterization of the binding reactivity of CRP for polycations and suggest a relationship between this binding site and the sites for calcium and phosphocholine. We propose that CRP-polycation interactions in the presence of phosphocholine may have physiologic significance during the acute inflammatory process.