Factor X

Factor X, also known by the eponym Stuart–Prower factor, is an enzyme (EC 3.4.21.6) of the coagulation cascade. It is a serine endopeptidase (protease group S1, PA clan).

Physiology

Factor X is synthesized in the liver and requires vitamin K for its synthesis.

Factor X is activated, by hydrolysis, into factor Xa by both factor IX (with its cofactor, factor VIII in a complex known as intrinsic Xase) and factor VII with its cofactor, tissue factor (a complex known as extrinsic Xase). It is therefore the first member of the final common pathway or thrombin pathway.

It acts by cleaving prothrombin in two places (an arg-thr and then an arg-ile bond), which yields the active thrombin. This process is optimized when factor Xa is complexed with activated co-factor V in the prothrombinase complex.

Factor Xa is inactivated by protein Z-dependent protease inhibitor (ZPI), a serine protease inhibitor (serpin). The affinity of this protein for factor Xa is increased 1000-fold by the presence of protein Z, while it does not require protein Z for inactivation of factor XI. Defects in protein Z lead to increased factor Xa activity and a propensity for thrombosis.

Factor X (disambiguation)

Factor X, also known as Stuart-Prower factor or as thrombokinase, is an enzyme.

Factor X may also refer to:

See also

El Factor X

El Factor X is the Colombian television music competition to find new singing talent. It is the based on the original British competition The X Factor, created by Simon Cowell. It is the first version produced in Latin America.

The show started screening in September 2005. The judges were Marbelle, singer Juan Carlos Coronel, and José Gaviria, a producer who has worked with stars like Carlos Santana. The winner was Julio César Meza. A second series followed in 2006 won by Francisco Villarreal and a third one, after a 2-year hiatus, in 2009 won by the duo Siam. The show will come back in 2012 for a fourth season, again after a hiatus of another 2 years.

All seasons and versions of the show have been hosted by the Colombian TV host and top model Andrea Serna, produced by Teleset and broadcast on RCN TV.

The show had two spin-offs. One was the one-year series El Factor X: Batalla de las Estrellas (meaning the Battle of the Stars). It was broadcast in 2006 and was won by Luz Amparo Álvarez.

Pre-exponential factor

In chemical kinetics, the pre-exponential factor or A factor is the pre-exponential constant in the Arrhenius equation, an empirical relationship between temperature and rate coefficient. It is usually designated by A when determined from experiment, while Z is usually left for collision frequency.

For a first-order reaction, it has units of s⁻¹. For that reason, it is often called frequency factor.

The frequency factor, A, depends on how often molecules collide when all concentrations are 1 mol/L and on whether the molecules are properly oriented when they collide.

Values of A for some reactions can be found in here.

References

IUPAC Gold Book definition of pre-exponential factor