Interaction of adenosine and adenylnucleotides with the human platelet membrane. Further characterization of the ADP binding sites.

The binding of adenosine and adenylnucleotides to the human platelet membrane has been measured and the subsequent effect on the binding of 14C-ADP has been determined. The following conclusions have been drawn: (1) Two reactions with different velocities (t 1/2 = 15--30 sec and t 1/2 = 4--6 min) seem to be involved in the binding of ADP to the platelet membrane. (2) AMP binds to the platelet membrane and partially inhibits binding of ADP in a competitive manner. These two findings suggest that ADP binding sites on the platelet membrane may be of more than one type. (3) At concentrations up to 10(-5) M, ATP does not itself bind to the platelet membrane but is rapidly transformed into ADP which, in turn, binds to the membrane and inhibits the binding of 14C-ADP. (4) Adenosine does not significantly interfere with the binding of 14C-ADP and has not been shown to bind to the platelet membrane.