Further characterization of human platelet ADP binding sites using 5'AMP. Demonstration of a highly reactive population of sites

Abstract

The binding of AMP and ADP to specific sites on the human platelet membrane have been compared. Although the two nucleotides bound to the platelet membrane with similar affinities (Ka ⋍ 0.4 × 10 6M −1), AMP binding was more rapid than ADP binding and involved a reduced number of binding sites. AMP competitively inhibited ADP binding by reacting with approximately half of its binding sites. Thus, the binding of AMP to specific sites in human platelet membrane provides a tool to differentiate two different types o£ ADP binding sites with similar affinities. AMP does not inhibit membrane nucleoside diphosphokinase, the enzyme which converts ADP into ATP when intact washed platelets or isolated platelet membranes are incubated with ADP in presence of divalent cations.