[15] Fibrin-stabilizing factor (factor XIII)

Fibrin-stabilizing factor (FSF, factor XIII) is the inactive precursor in blood plasma for the enzyme fibrinoligase (activated FSF, FXIIIa). This transamidase performs the essential hemostatic function of catalyzing the formation of intermolecular 7-glutamyl-c-lysine bridges between fibrin molecules, which greatly augments the physical stiffness of the clot structure and its resistance to lysis. The enzyme may also be involved in strengthening the attachment of the fibrin network to the disrupted platelet membranes and to the surface of fibroblasts, the latter being conceivably important in wound healing. During coagulation, the fibrin-stabilizing factor zymogen is converted to the active enzyme in two distinct consecutive steps. The first requires only thrombin, and the second involves a specific interaction of the thrombin-modified zymogen with calcium ions only. This chapter discusses the slightly modified method of the original method for obtaining factor XIII from citrated outdated blood bank human plasma (or oxalated bovine plasma) by a salt-gradient DEAE-Cellulose chromatographic procedure, as described by Lorand and Gotoh. This procedure has been widely used in clinical research, for the genetic appraisal of hereditary factor XIII deficieney; for evaluating transfusions administered to the deficient individual for identifying circulating acquired inhibitors in hemorrhagic disorders of fibrin stabilization.