The object of the proposed research is to extend knowledge of the blood platelet release glycoprotein, thrombospondin (TSN) by chemical and immunochemical characterization, by establishment of relationships between TSN release and its level in normal circulating blood, and by determining the function of this glycoprotein in homeostasis. Specifically, peptide mapping, separation and sequencing will be continued with the aid of monoclonal antibodies, now under development by us, which are directed against specific paptide regions of TSN. The monoclonal antibodies will be used in purification, for molecular mapping by electron microscopy, and in further analytical radioimmunoassays, both on circulating blood and on other normal and pathological body fluids. Electron microscope mapping studies, utilizing specific markers such as IgG-Fab, lectins and liganded mucopolysaccharides, are expected to relate certain immunochemical loci on TSN to the tertiary structure of the molecule. The specificity of TSN interactions with mucopolysaccharides, and possibly also with proteins such as collagen, fibrinogen, fibronectin and von WIllebrand's protein, will be explored in binding experiments, by electron microscopy, and in terms of peptide chemistry. The effects of cross-linking agents will be studied. Finally, relationships of TSN and its complexes to subendothelial and platelet surfaces will be explored at wound sites, in in vitro coagulation systems, and animal models by means of both light and electron immunohistochemical techniques.