Factor VIII
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 . 
<triplet> Factor VIII <subj> blood coagulation <obj> biological process <triplet> factor IX <subj> blood coagulation <obj> biological process <triplet> factor X <subj> blood coagulation <obj> biological process