  factor viii (fviii) is an essential blood-clotting protein, also known as anti-hemophilic factor (ahf). in humans, factor viii is encoded by the f8 gene. defects in this gene results in hemophilia a, a recessive x-linked coagulation disorder. factor viii is produced in liver sinusoidal cells and endothelial cells outside of the liver throughout the body. this protein circulates in the bloodstream in an inactive form, bound to another molecule called von willebrand factor, until an injury that damages blood vessels occurs. in response to injury, coagulation factor viii is activated and separates from von willebrand factor. the active protein (sometimes written as coagulation factor viiia) interacts with another coagulation factor called factor ix. this interaction sets off a chain of additional chemical reactions that form a blood clot. factor viii participates in blood coagulation; it is a cofactor for factor ixa which, in the presence of ca2+ and phospholipids forms a complex that converts factor x to the activated form xa. the factor viii gene produces two alternatively spliced transcripts. transcript variant 1 encodes a large glycoprotein, isoform a, which circulates in plasma and associates with von willebrand factor in a noncovalent complex. this protein undergoes multiple cleavage events. transcript variant 2 encodes a putative small protein, isoform b, which consists primarily of the phospholipid binding domain of factor viiic. this binding domain is essential for coagulant activity.{{cite web | title = entrez gene: f8 coagulation factor viii, procoagulant component (hemophilia a)| url =http://www.ncbi.nlm.n
Acute_phase_proteins Coagulation_system Cofactors Human_proteins Recombinant_proteins