The objective of this project is to purify a hepatic vitamin K-coumarin binding protein(s) which regulates the plasma concentrations of the vitamin K dependent clotting factors II, VII, IX and X. Determination of this protein(s) binding characteristics for vitamin K and coumarin anticoagulants and determination of its catalytic function $ will help clarify the mode of action of vitamin K and coumarin anticoagulants. The approach is to simultaneously purify the binding protein from both Sprague-Dawley (SD) and warfarin resistant (WR) rats, the latter being 50-200 times less sensitive to the anticoagulant action of warfarin and serving as excellent negative controls. A protein has been purified from a 0.2-0.4 m KC1 wash of rat liver ribosomes on DEAE cellulose columns. The protein is 80-90% pure, approximately 30,000 molecular weight and binds 12-30 times more warfarin when extracted from SD rats than from WR rats. The Km for half-saturation for the SD protein is 8 micron m warfarin. The optimal pH for binding is 7.3. The protein is not a true ribosomal protein, but rather is of membranous origin and attaches to ribosomes in the presence of deoxychocate. BIBLIOGRAPHIC REFERENCE: M.T. Searcey and C.B. Graves. Sub-cellular Distribution of Warfarin-Binding Protein from Sprague-Dawley and Warfarin-Resistant Rats. Fed. Proc. 35, 1763, 1976.