Hydrolyzes extracellular Ap3A into AMP and ADP, and Ap4A into AMP and ATP. Ap3A and Ap4A are diadenosine polyphosphates thought to induce proliferation of vascular smooth muscle cells. Acts as a procoagulant, mediating platelet aggregation at the site of nascent thrombus via release of ADP from Ap3A and activation of ADP receptors. H2O + P(1),P(3)-bis(5'-adenosyl) triphosphate = ADP + AMP + 2 H(+) Binds 2 Zn(2+) ions per subunit. Expressed on the surface of vascular endothelia. Belongs to the nucleotide pyrophosphatase/phosphodiesterase family.