Protein S and thrombosis

Thrombosis is a serious problem in the United States. Activated protein C is a vitamin K-dependent serine protease that seems to be an important regulator of the hemostatic process. Protein S is another vitamin K-dependent protein that is essential for the expression of the anticoagulant activity of activated protein C. Evidence suggests that defects in either of these proteins may be related to the development of thrombosis. Therefore, the accurate measurement of these proteins is important in the study and in the treatment of thrombosis. Sixty percent of the protein S found in human plasma is bound to the complement component C4b-binding protein, and when in this complex, protein S is inactive. The remaining 40 percent is the free, functional form of protein S. This paper describes the measurement of both free and total protein S by two types of assays. The first assay involves immunoelectrophoresis, also known as the Laurell Rocket method. The second assay is a capture enzyme linked immunosorbent assay (ELISA). The two assays are compared as to relative ease and cost.