Biochemical and functional comparison of platelet and raji cell clq receptors

Previous studies have suggested that platelet Clq receptors share a variety of structural and functional similarities with Clq receptors isolated from Raji cells. The present study extends these observations and demonstrates similar migration of platelet and Raji cell receptors in 7.5% SDS-polyacrylamide gels, as well as similarities in amino acid composition and receptor migration on cellulose acetate electrophoresis at pH 8.6. Moreover, direct functional comparisons were performed to assess receptor reactivity with immobilized Clq and collagen, as structural similarities between collagen and the amino terminus of Clq involved in receptor binding are well known, and Clq inhibits collagen-induced platelet aggregation. Like the platelet Clq receptor, Clq receptors from Raji cells demonstrated enhanced reactivity with Clq relative to collagen-coated surfaces. These interactions were highly susceptible to manipulation of the ionic strength of the buffer medium. Clq receptor recognition of collagen was considerably more sensitive to increasing NaCl concentrations than were receptor interactions with Clq. Platelet and Raji cell Clq receptor adhesion to Clq-coated surfaces occurred at physiologic ionic strength, whereas receptor interactions with collagen were completely inhibited in the presence of greater than 60 mM NaCl. These data suggest that both purified platelet and Raji cell Clq receptors exhibit increased avidity for immobilized Clq as compared to collagen. The biochemical and functional similarities between these receptors support the concept that Clq receptors on platelets and Raji cells may be related.