FIXa variant:FVIIIa does not convert FX to the active FXa

Stable Identifier
Reaction [transition]
Homo sapiens
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Factor IX (FIX) is a vitamin K-dependent trypsin-like serine protease zymogen in plasma, which upon activation to its active form (FIXa), binds to cofactor VIIIa (FVIIIa) on negatively charged membrane surfaces in the presence of Ca2+ to activate factor X (FX) in the intrinsic pathway of the blood clotting cascade (Davie EW et al. 1991; Ngo JC et al. 2008). FIX deficiency is associated with mild to severe bleeding in hemophilia B (HB) patients (Rallapalli PM et al. 2013). HB is caused by a wide range of mutations that can include point mutations (nonsense and missense), insertions, deletions and other complex rearrangements of the F9 gene (Rallapalli PM et al. 2013). Exons 7 and 8 encode the catalytic domain of FIX, which is responsible for the subsequent activation of FX in the coagulation cascade. Disease-causing mutations at these exons 7 and 8 produce dysfunctional FIX with impaired clotting enzyme activity (Usharani P et al. 1985: Attree O et al. 1989; Bajaj SP et al. 1990; Spitzer SG et al. 1990; Ludwig M et al. 1992; Lu Q et al. 2015). The Reactome event describes failed generation of FXa as the functional consequence of the defective serine protease activity of hemophilia B (HB)-associated FIX variants such as G363R & G363E (Lu Q et al. 2015), G357E (Miyata T et al. 1991), A436V (Usharani P et al. 1985), I443T (Hamaguchi N et al. 1991), G409V (Bajaj SP et al. 1990), D410H and S411G (Ludwig M et al. 1992).
Literature References
PubMed ID Title Journal Year
2105717 Replacement of isoleucine-397 by threonine in the clotting proteinase factor IXa (Los Angeles and Long Beach variants) affects macromolecular catalysis but not L-tosylarginine methyl ester hydrolysis. Lack of correlation between the ox brain prothrombin time and the mutation site in the variant proteins

Warn-Cramer, BJ, Spitzer, SG, Bajaj, SP, Kasper, CK

Biochem. J. 1990
1346975 Hemophilia B caused by five different nondeletion mutations in the protease domain of factor IX

Ludwig, M, Brackmann, HH, Smith, KJ, Birktoft, JJ, Sabharwal, AK, Olek, K, Bajaj, SP

Blood 1992
1958666 Factor IX Amagasaki: a new mutation in the catalytic domain resulting in the loss of both coagulant and esterase activities

Mitsui, K, Naka, H, Sugimoto, M, Kamiya, K, Umeyama, H, Yoshioka, A, Fukui, H, Sakai, T, Miyata, T, Yamamoto, K

Biochemistry 1991
26023895 Expression and Characterization of Gly-317 Variants of Factor IX Causing Variable Bleeding in Hemophilia B Patients

Wang, X, Rezaie, AR, Yang, L, Lu, Q, Manithody, C

Biochemistry 2015
3965513 Characterization of three abnormal factor IX variants (Bm Lake Elsinore, Long Beach, and Los Angeles) of hemophilia-B. Evidence for defects affecting the latent catalytic site

Warn-Cramer, BJ, Usharani, P, Bajaj, SP, Kasper, CK

J. Clin. Invest. 1985
7803238 Factor IX Bm Kiryu: a Val-313-to-Asp substitution in the catalytic domain results in loss of function due to a conformational change of the surface loop: evidence obtained by chimaeric modelling

Matsui, A, Kato, H, Matsusue, T, Kamiya, K, Umeyama, H, Yoshioka, A, Komooka, H, Kuze, K, Miyata, T

Br. J. Haematol. 1994
2303434 Experimental and theoretical evidence supporting the role of Gly363 in blood coagulation factor IXa (Gly193 in chymotrypsin) for proper activation of the proenzyme

Welsh, WJ, Warn-Cramer, BJ, Birktoft, JJ, Spitzer, SG, Kasper, CK, Bajaj, SP

J. Biol. Chem. 1990
Catalyst Activity

serine-type endopeptidase activity of factor VIIIa:factor IXa variant [plasma membrane]

Normal reaction
Functional status

Loss of function of factor VIIIa:factor IXa variant [plasma membrane]

Name Identifier Synonyms
hemophilia B DOID:12259 factor IX deficiency, Congenital factor IX deficiency, deficiency, functional factor IX, Congenital factor IX disorder
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