C-Reactive Protein Induced Agglutination of Lipid Suspensions Prepared in the Presence and Absence of Phosphatidylcholine1

Abstract

CRP-induced agglutination of lipid suspensions prepared in the presence and absence of phosphatidylcholine was studied by a newly devised quantitative method. CRP caused as much agglutination of suspensions composed of egg yolk phosphatidylcholine, cholesterol, and Span 60 as of those composed of cholesterol and Span 60, suggesting that phosphocholine residues of phosphatidylcholine are not important as binding sites for CRP. Agglutination of suspensions prepared without phosphatidylcholine was inhibited by phosphocholine, indicating that the inhibition by phosphocholine is non-competitive. Although phosphatidylcholine is not an essential component for agglutination of suspensions, it may modify the mode of interaction of CRP with its binding site on lipid suspensions, since the sensitivity of the agglutination to phosphocholine and the Ca²⁺ requirement were influenced by the presence of phosphatidylcholine in the suspensions.