Factor viii

Factor VIII consists of two subunits connected by calcium:

• the low molecular weight portion VIII C
• and
• the high-molecular F-VIII-associated protein, the FVII RvWF.

The coagulation active component is the F-VIII C.

Thrombin activates the F-VIII enzymatically by splitting off peptides. The molecular weight of F-VIII C is 268 kD, the plasma concentration is 0.15 mg/l.
Factor VIII C is a non-enzymatic cofactor of the complex of factor IXa, phospholipids and calcium. This complex is called tenase. Tenase catalyses the proteolytic activation of factor X and increases its activity many thousands of times over.

Factor VIII is synthesized in the liver. Factor VIII is encoded by the F-VIII gene located on the X chromosome. Deficient production or a functional disorder of factor V III C leads to "haemophilia A".
The high-molecular factor VIII forms a complex with the von Willebrand factor, which essentially causes the aggregation of the thrombocytes. It is known as the F-VIII-vWF complex. The synthesis takes place in the endothelium and in the thrombocytes. The molecular weight is over 1 million Dalton.

Subunits of the F-VIII are:

• VIII C Cofactor of Tenase
• VIII R:WF von Willebrand factor
• VIII R:Rco Ristocetin cofactor activity (activity for the ristocetin-induced activity)
• VIII R:Ag F-VIII-associated antigen I, reacts with antibodies against F-VIII
• VIII AG I immunologically different from VIII R:Ag
• VIII C:Ag reacts with homologous antibodies

1. HA Neumann (2014) The coagulation system. ABW-Wissenschaftsverlag GmbH Berlin S. 59f.