We intend to utilize sensitive fluorescence and NMR methods to evaluate interactions of metal ions, phospholipids, and lipoproteins with prothrombin and coagulation factors II and X. We will evaluate paramagnetic probes such as Mn (II) and Gd (III), as well as the fluorescent probe Tb (III), as potential substitutes for Ca (II) in order to obtain information as to the role of the metal ion binding site in phospholipid-coagulation protein interactions. Additionally, we wish to utilize fluorescence, NMR, and pulsed laser methods to evaluate the nature of the conformational changes produced in prothrombin and factor X, upon cooperative interactions with certain metal ions.