CHARACTERIZATION OF PROTEIN DISULFIDE-ISOMERASE RELEASED FROM ACTIVATED PLATELETS

Protein disulphide isomerase (PDI) activity is released by activated p latelets, Ln this study, PDI was purified from platelets and found to have an apparent mass, pi and N-terminal sequence similar to those for other human PDIs. Rabbit antibodies were generated and used to establ ish that, on activation, platelets release a protein immunologically i dentical to PDI: in platelets, Approximately 10% of total platelet PDI was released by thrombin and 20% by calcium ionophore, The antibody w as used to demonstrate PDI on the external surface of platelets by ele ctron microscopy. Flow cytometry was used to demonstrate that upon act ivation of platelets with ionophore PDI was released by vesiculation. Since platelets are present and become activated at sites of vascular injury, platelet PDI may play a role in the various haemostatic and ti ssue remodelling processes in which platelets are involved.