The factor Xa-catalyzed activation of factor V

Area of Science:

• Biochemistry
• Hematology
• Molecular Biology

Background:

• Factor V is a procofactor with significantly lower activity than its activated form, Factor Va.
• Thrombin typically catalyzes the conversion of Factor V to Factor Va, but its initial role in prothrombinase activity is unclear.
• Understanding the initial activation of Factor V is crucial for comprehending thrombin generation.

Purpose of the Study:

• To investigate the activation of Factor V by Factor Xa.
• To determine if Factor Xa can catalyze the conversion of Factor V to an active cofactor.
• To elucidate the role of Factor Xa in initiating prothrombinase activity.

Main Methods:

• Assessed cofactor activation by monitoring thrombin generation using a fluorescent substrate (DAPA).
• Utilized immunoadsorption to remove trace amounts of Factor Va and confirm Factor Xa specificity.
• Incubated Factor V with Factor Xa in the presence of vesicles, CaCl2, and DAPA.

Main Results:

• Factor Xa catalyzed a time-dependent increase in Factor V cofactor activity.
• Phosphatidylcholine/phosphatidylserine vesicles enhanced the rate of Factor V activation by Factor Xa.
• Activation was dependent on Factor Xa and produced different products than thrombin-catalyzed activation.

Conclusions:

• Factor Xa directly catalyzes the activation of Factor V.
• This Factor Xa-mediated activation of Factor V may be responsible for early prothrombinase activity.
• The findings provide new insights into the initiation of the coagulation cascade.