Platelet thrombus formation appears to be mediated at the platelet surface. However, it is not clear how the platelet membrane receives and transmits information leading to the aggregation and release phenomenon. The long range goal of my study is an understanding of the molecular events at the platelet surface during the generation of a platelet thrombus. Platelet membrane preparations contain three or four recognized glycoproteins which have been shown to have surface orientation. My research program will include purification and characterization of the membrane glycoproteins, and a study of their conformation within the membrane. One important goal will be to determine whether the glycoproteins traverse the bilipid layer and extend reactive groups onto the cytoplasmic surface. The glycoproteins will also be studied for their possible role as receptors for specific aggregating agents such as thrombin and collagen. This will be approached by looking for changes in both glycoprotein structure and availability of reactive sites in response to these aggregating agents. The antigenicity of the surface glycoproteins will also be studied for its possible role in the production of isoimmune, autoimmune, and drug-immune thrombocytopenias.