Differentiation of antihemophilic factor (AHF) and von Willebrand factor (vWF) by their interaction with urea and selected amino acids

Chromatography of the VIII/vWF complex on dextran sulphate sepharose

The applicability of Dextran Sulphate (DS) agarose in the purification of the VIII/vWf complex from cryoprecipitate was investigated. The elution profiles indicate high affinity of the VIII/vWf complex for the matrix. With application of combined salt/pH gradients good resolution of VIII/vWf from most of the applied proteins can be achieved. VIII/vWf normally elutes as a single component (70-90% vWf:Ag and vWf:RCo) with modest yields of factor VIII (30-40%) VIII:C and 50-70% VIII:Ag) providing calcium ions are present. Addition of L-lysine, Histidine and Arginine (all 1.0M) inhibit binding of proteins to the matrix. Alternatively, higher yields of VIII:C can be obtained (80% VIII:C and 100% VIII:Ag) by the application of L-lysine gradients (0-0.6M) but with loss of resolution from Fn and slight dissociation of VIII:C from vWf:Ag.

Factor VIII binds to von Willebrand factor via its Mr-80,000 light chain

The formation of a complex between factor VIII (FVIII) and von Willebrand factor (vWF) was studied using purified radiolabeled human FVIII and purified human vWF. A binding assay was developed in which vWF was coated on microtiter wells. FVIII was shown to bind specifically and reversibly to the immobilized vWF. At a coating of 70 pg vWF/well, binding was half-maximal at a FVIII concentration of 70 +/- 10 pM. In order to ascertain which part of FVIII interacted with vWF, eight monoclonal antibodies, directed against FVIII, were tested for their ability to inhibit FVIII-vWF interaction. One of the eight antibodies, CLB-CAg:58, inhibited binding completely. This antibody was demonstrated to react with the Mr-80,000 light chain of FVIII. Direct evidence for the involvement of this chain in vWF binding was obtained by studying the binding of isolated, radiolabeled FVIII heavy and light chains. In a typical experiment 23-30% of the radioactivity bound when the FVIII light chain was added and less than 1% when the FVIII heavy chain was added.

The physiology and pathophysiology of the factor VIII complex

The factor VIII complex consists of two noncovalently linked proteins: von Willebrand factor (VWF) and factor VIII (FVIII). VWF plays an important role in primary hemostasis by mediating the adherence of blood platelets to the damaged vessel wall. A review of the literature on VWF is given with regard to its physicochemical properties and mode of action. FVIII acts as a cofactor in the factor Xa-generating enzyme complex of the intrinsic coagulation cascade. Starting with the recently published primary structure of FVIII, the literature is reviewed for structural information on FVIII. Also, an effort is made to characterize the interaction of FVIII with VWF and to discuss the possible physiological significance of FVIII-VWF complex formation. Interaction of FVIII with the clotting factors of the intrinsic pathway of coagulation is described in detail. Hemophilia and von Willebrand's disease (VWD) are both congenital bleeding disorders affecting a great many people. The different variants of these diseases are described with some reference to therapy and detection.