LOCALIZATION OF PROTEIN DISULFIDE-ISOMERASE TO THE EXTERNAL SURFACE OF THE PLATELET PLASMA-MEMBRANE

Protein disulfide isomerase (PDI) is an enzyme that catalyzes the form ation as well as the isomerization of disulfide bonds. In this study, antibodies against PDI were used to show PDI antigen on the platelet s urface by indirect immunofluorescence microscopy and by flow cytometry . The platelets were not activated, as evidenced by the absence of sta ining by an antibody against P-selectin. Permeabilized platelets showe d little cytosolic PDI by indirect immunofluorescence microscopy, sugg esting that the majority of platelet PDI is localized to the platelet surface. PDI activity against ''scrambled'' RNase was shown with intac t platelets. The activity was inhibited by inhibitors of PDI and by an antibody against PDI. Other blood cells showed little PDI, Platelet s urface PDI may play a role in the various physiological and pathophysi ologic processes in which platelets are involved. (C) 1995 by The Amer ican Society of Hematology.