A glycoprotein synthesized in the liver which contains 12 Gla residues that are dependent on vitamin K for biosynthesis. The zymogen, FIX, is converted to a serine protease (FIXa) by the enzyme FXIa. FIXa participates in the intrinsic pathway of coagulation by converting FX to FXa in the presence of FVIIIa, phospholipid, and calcium (tenase complex). The gene for FIX is X-linked and mutations in the gene give rise to a bleeding disorder, Hemophilia B. The slide show entitled Coagulation Pathways (All Components) shows how FIX relates to the other coagulation factors. See also the slide show entitled Intrinsic Pathway-APTT.
