The overall objective of the proposed reserach is to elucidate the mechanism whereby heparin and related glycosaminoglycans interact with circulating proteins that promote or suppress blood coagulation. The specific focus of our investigations will be on the interaction of antithrombin with thrombin and coagulation- factor Xa, and the actions of heparin on these processes. One aspect of the work, therefore, will be on the structural characteristics of heparin and analogous compounds, and the relation of their specific chemical structure with biological activity. The other facet will be on structure of antithrombin as it relates to its interaction with the procoagulants and with heparin. Detailed investigations will be performed on specific fractions on heparins and heparan sulfates from different animal and tissue sources with the purpose of defining the location of certain units or sequences within its polymeric chain. Our approach will utilize novel procedures involving the structural characterization of the glycosaminoglycans in their native proteglycan form, while they are linked to specified insoluble matrices. Heparin segments defined in terms of chemical properties and location within the chain, will be characterized with respect to the effect on coagulation process and other biological activities. The studies on the structure of antithrombin will deal mainly with delineating the sites and polypeptide segment(s) that interact with thrombin, factor Xa and heparin. For this purpose we will utilize well-defined fragments of antithrombin obtained after chemical and enzymatic degradations. Heparin is of considerable interest because of its high anticoagulant potency and its clinical use in the treatment and prevention of thromboses. Moreover, since heparin appears to mimic certain glycosaminoglycans of endothelial cells, elucidation of its mechanism of action should clarify some of the physiologic factors that control or modulate coagulation processes.
