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Factor VIII: Structure and function in blood clotting
Author(s) -
Chavin Stephen I.
Publication year - 1984
Publication title -
american journal of hematology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.456
H-Index - 105
eISSN - 1096-8652
pISSN - 0361-8609
DOI - 10.1002/ajh.2830160312
Subject(s) - factor ixa , factor x , chemistry , thrombin , von willebrand factor , factor ix , clotting factor , factor v , glycoprotein , factor vii , platelet , biochemistry , coagulation , medicine , thrombosis
Factor VIII (antihemophilic factor) is the protein that is deficient or defective in patients with classical hemophilia and Von Willebrand syndrome. Factor VIII in plasma is thought to be associated in a complex with the highest molecular weight multimers of another glycoprotein, Von Willebrand protein. Highly purified human factor VIII appears to have an M r of between 200, 000 and 300,000 and to consist of several polypeptide chains. The concentration of factor VIII in plasma is around 100‐200 ng/ml, equivalent to around 1 nM. The purified proteins retain one or more of the known properties of factor VIII, including the acceleration of factor IX a ‐mediated activation of factor X, ability to be activated by thrombin and factor X a , inactivation by activated protein C, and by human antibodies to factor VIII. Among the known clotting factors, factors VIII and V are exceptional in not possessing enzymatic activity. Factors IX 3 and VIII and X appear to form a functional complex, all of which need to be present and active simultaneously for optimal activation of factor X. The mechanism by which factor VIII promotes activation of factor X by factor IX a is not known, but the major effect is to increase the rate of the reaction. Following treatment of factor VIII with thrombin, a new and smaller polypeptide M r around 70,000 ± 5,000 is produced. Factors IX a and X a also have been reported to activate factor VIII. It is not known whether limited proteolytic cleavage is required absolutely for the expression of factor VIII activity or if it only increases an activity already expressed by the uncleaved protein. Factor VIII is inactivatd by thrombin and by activated protein C. Thus, factor VIII can be modulated by at least four of the serine proteases in the clotting system. A major goal for future research is to increase our understanding of the role in blood clotting played by factor VIII, and to apply this information to clinical problems which result from inherited abnormalities of factor VIII.