Binding of bovine coagulation factor Xa to platelets

Area of Science:

• Biochemistry
• Hematology
• Cell Biology

Background:

• Platelets play a critical role in hemostasis and thrombosis.
• Coagulation factor Xa (FXa) is a key enzyme in the coagulation cascade.
• Understanding FXa-platelet interactions is vital for hemostasis research.

Purpose of the Study:

• To investigate the binding characteristics of bovine coagulation factor Xa to bovine platelets.
• To identify the conditions under which FXa binds to platelets.
• To elucidate the role of FXa-platelet interaction in thrombin generation.

Main Methods:

• Studied the binding of 125I-labeled bovine factor Xa to washed bovine platelets.
• Induced platelet release reaction using thrombin or calcium ionophore A 23187.
• Assessed binding saturation, reversibility, and kinetics.

Main Results:

• FXa binds to a specific platelet receptor accessible after activation.
• Binding is saturable, reversible, and correlates with thrombin formation rate.
• Estimated 290-420 binding sites/platelet with an association constant of 2.8 x 10^9 to 1.0 x 10^10 M^-1.
• Diisoprophyl fluorophosphate-FXa binds to the same site, indicating no proteolysis required.
• FXa binding is rapid, similar to hormone-receptor binding.
• FXa-platelet interaction enhances prothrombin activation.

Conclusions:

• Activated platelets possess a specific receptor for coagulation factor Xa.
• This interaction significantly contributes to thrombin generation and prothrombin activation.
• FXa-platelet binding is a rapid and efficient process crucial for coagulation.