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Factor IX

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Official Full Name
Factor IX
Background
The zymogen factor IX is a single chain vitamin K-dependent glycoprotein which is synthesized in the liver. The domain structure of factor IX is similar to that of the other vitamin K dependent coagulation factors. The NH2-terminal region contains 12 γ-carboxyglutamic acid (gla) residues which facilitate the calcium dependent binding of factor IX to negatively charged phospholipid surfaces. Two domains which are homologous to epidermal growth factor (EGF) span the region between the NH2-terminal gla domain and the activation peptide (Ala-146 to Arg-180). Factor IX is activated by either factor XIa or the factor VIIa/tissue factor/phospholipid complex. Cleavage at site A (see figure) yields the intermediate IXa which is subsequently converted to the fully active form IXaβ by cleavage at site B. The NH2-terminal light chain (GLA and EGF domains) remains covalently attached to the COOH-terminal heavy chain by a disulfide bond. The serine protease catalytic triad (Ser-365, His 221, Asp-269) is located in the heavy chain. Factor IXaβ is the catalytic component of the "intrinsic factor Xase complex" (factor VIIIa/IXa/Ca2+/phospholipid) which proteolytically activates factor X to factor Xa. Human factor IX is prepared from fresh frozen plasma by a combination of conventional procedures and immunoaffinity chromatography. Bovine factor IX is prepared from fresh citrated bovine plasma by a modification of the method described by Fujikawa et al. The purified proteins are supplied in 50% (vol/vol) glycerol/H2O and should be stored at -20°C. Purity is determined by SDS-PAGE analysis and activity is measured using a factor IX clotting assay.
Synonyms
Human Factor IX; Factor IX
Catalog Product Name EC No. CAS No. Source Price
CZY-032 Mouse factor IX Mouse Inquiry
CZY-003 Bovine factor IX 9001-28-9 Bovine Inquiry
CZY-002 Human Factor IX 9001-28-9 Human Inquiry

Related Reading

Introduction

Factor IX is a critical component of the human blood coagulation system, often recognized by its alternate name, Christmas Factor, after Stephen Christmas, the first person diagnosed with hemophilia B. Structured as a vitamin K-dependent serine protease, this vital enzyme plays a quintessential role in the blood clotting cascade, aiding the body's self-healing mechanism. When injuries occur, leading to bleeding or hemorrhage, Factor IX combined with other clotting factors work in tandem to form clots and halt bleeding. Any aberration in Factor IX can lead to severe bleeding disorders, such as Hemophilia B, underscoring the clinical significance of Factor IX.

Structure

Factor IX is synthesized by the liver and appears as a zymogen, or inactive enzyme, before it is activated via catalytic cleavage. Structurally, it possesses a heavy chain and a light chain, linked by a disulphide bond. It features several domains including the GLA (gamma-carboxyglutamic acid) domain, two epidermal growth factor-like (EGF-like) domains, and a serine protease domain. Interestingly, the GLA domain allows Factor IX to bind to phospholipid membranes in a calcium-dependent manner, effectively localizing the coagulation cascade to the site of injury.

Functions

The function of Factor IX extends beyond simple protein synthesis. It activates Factor X, the pivotal point in the coagulation cascade where the intrinsic and extrinsic pathways converge, and this believe to be its primary biological role. Upon activation, Factor X catalyzes the conversion of prothrombin to thrombin, a substance that clots blood by converting soluble fibrinogen into insoluble fibrin strands. This process implies the instrumental role of Factor IX in ensuring rapid, localized clotting to minimize blood loss during injury.

Mechanism

The mechanism through which Factor IX operates is complex and precisely controlled to prevent unwarranted coagulation. The activation of Factor IX is facilitated by Factor VIII, in a process requiring calcium ions and phospholipids. Notably, the activated Form IX (FIXa) then forms a complex with Factor VIII on the surface of activated platelets – sometimes referred to as the "tenase" complex – which acts to activate Factor X.

Applications

Over the years, the clinical applications of Factor IX have evolved, with a crucial role in the management and prophylaxis of bleeding in patients with Hemophilia B. Recombinant FIX (rFIX) is a mainstay of hemophilia B therapy, and extended half-life (EHL) rFIX prodrugs have recently been introduced. In gene therapy studies, a modified version of the FIX gene is delivered into the patient's liver cells, establishing a new paradigm for a potential cure rather than treatment.

Clinical Significance

The clinical significance of Factor IX cannot be overstated. Its deficiency or dysfunction often culminates in Hemophilia B, a hereditary bleeding disorder. Hemophilia B is also sometimes classified as Christmas disease, named after Stephen Christmas, the first known person diagnosed with FIX deficiency. Furthermore, the overactive variants of FIX could potentially lead to an increased risk of thrombosis, providing an intriguing area for future research.

Conclusion

Factor IX grants a privileged insight into the intricate yet efficient process of blood clotting. Its critical role in coagulating blood, combined with its impact on health when deficient or dysfunctional, illuminates the need for continued advancements in our understanding and manipulation of Factor IX. Despite the progress made, future research promises to further elucidate the complexities of Factor IX.