Factor IX is a vitamin K-dependent plasma protein that participates in the intrinsic pathway of blood coagulation by converting factor X to its active form in the presence of Ca(2+) ions, phospholipids, and factor VIIIa. Selective cleavage of Arg-|-Ile bond in factor X to form factor Xa. Heterodimer of a light chain and a heavy chain; disulfide-linked (PubMed:20121198, PubMed:20121197, PubMed:20080729). Interacts with SERPINC1. Detected in blood plasma (at protein level) (PubMed:3857619, PubMed:8295821, PubMed:2592373, PubMed:9169594, PubMed:19846852). Synthesized primarily in the liver and secreted in plasma. Calcium binds to the gamma-carboxyglutamic acid (Gla) residues in the Gla domain. Calcium can also bind, with stronger affinity, to another site beyond the Gla domain (PubMed:6425296). Under physiological ion concentrations, Ca(2+) is displaced by Mg(2+) from some of the gammaglutamate residues in the N-terminal Gla domain. This leads to a subtle conformation change that may affect the interaction with its binding protein (By similarity). Activated by factor XIa, which excises the activation peptide (PubMed:9169594, PubMed:1730085). The propeptide can also be removed by snake venom protease (PubMed:20004170, PubMed:20080729). The iron and 2-oxoglutarate dependent 3-hydroxylation of aspartate and asparagine is (R) stereospecific within EGF domains. The disease is caused by variants affecting the gene represented in this entry. Mutations in position 43 (Oxford-3, San Dimas) and 46 (Cambridge) prevents cleavage of the propeptide (PubMed:12588353, PubMed:2738071, PubMed:3009023, PubMed:8295821, PubMed:9169594, PubMed:9600455, PubMed:25251685). Mutation in position 93 (Alabama) probably fails to bind to cell membranes (PubMed:3790720). Mutation in position 191 (Chapel-Hill) or in position 226 (Nagoya or Hilo) prevent cleavage of the activation peptide (PubMed:6603618, PubMed:8076946, PubMed:12588353, PubMed:2162822, PubMed:25251685, PubMed:2713493). The disease is caused by variants affecting the gene represented in this entry. The disease is caused by variants affecting the gene represented in this entry. Available under the name BeneFix (Baxter and American Home Products). Used to treat hemophilia B. In 1952, one of the earliest researchers of the disease, Dr. R.G. Macfarlane used the patient's surname, Christmas, to refer to the disease and also to refer to the clotting factor which he called the 'Christmas Factor' At the time Stephen Christmas was a 5-year-old boy. He died in 1993 at the age of 46 from acquired immunodeficiency syndrome contracted through treatment with blood products. Belongs to the peptidase S1 family. Factor IX entry Clinical information on BeneFix The Christmas Factor - Issue 41 of December 2003