Calcium-dependent binding of tetranectin to fibrin.

The plasma protein, tetranectin, capable of binding to kringle-4 of plasminogen, is reduced in serum after clotting of plasma. Fibrin binding is confirmed by the presence of tetranectin in clot lysates. The amount of tetranectin bound to the fibrin varies with the plasma level, but constitutes a constant percentage of 13-17% of the plasma tetranectin. The fibrin binding of tetranectin requires the presence of CaCl2, but is independent of factor XIII. Further, it is independent of the presence and fibrin binding of plasminogen. Reduction of tetranectin in serum of fresh blood (9%) is less than reduction in serum made from platelet-poor plasma (13-17%). This difference could be attributed to a releasable platelet pool of tetranectin. Extracts of platelets show around 15% tetranectin (relative to the plasma concentration). It is concluded that tetranectin can, upon coagulation, be released from platelets and become partially bound to fibrin.