Factor IX activator will be prepared from bovine serum by procedures already published, and will be assayed by its ability to carry out the enzymatic activation of bovine factor IX. Specific goals proposed for this research project include the labelling of the factor IV activator with radioactive diisopropylphosphofluoridate, tryptic digestion of the inactivated enzyme, and preparation of the radiolabelled tryptic peptide in a pure form followed by determination of the amino sequence of this active site peptide. In related projects, work will continue on the determination of primary structure of other proteins involved in blood coagulation, including bovine alpha and beta thrombin.