Expression of LMW-PTP in human platelets. (A) Aliquots (40 μg) of whole platelet lysates from 4 different donors (A-D) were separated by SDS-PAGE on a 10% to 20% acrylamide gradient gel, transferred to nitrocellulose, and probed with a polyclonal antibody against LMW-PTP. As a control for the specificity of the anti–LMW-PTP antibody, platelet proteins from the donor A were analyzed by identical immunoblotting procedure, but in the absence of primary antibody (lane A* on the left). The band corresponding to LMW-PTP is indicated on the right, and the migration of molecular mass markers is reported on the left. (B) In order to quantify the amount of LMW-PTP expressed in platelets, immunoblotting analysis with the anti–LMW-PTP antibody was performed upon loading on the same gel of increasing amounts of total platelet proteins, corresponding to the indicated number of cells, and of known amounts of purified recombinant LMW-PTP.