The interactions between antithrombin III, thrombin and surface immobilized heparin

Area of Science:

• Biochemistry
• Biomaterials Science
• Surface Chemistry

Background:

• Antithrombin III (ATIII) is a crucial inhibitor of thrombin.
• Heparin immobilization on surfaces is used to modulate biological interactions.
• Understanding protein-surface interactions is vital for biomaterial development.

Purpose of the Study:

• To investigate the binding dynamics of ATIII and thrombin on immobilized heparin surfaces.
• To determine the factors influencing ATIII binding and thrombin inactivation.
• To elucidate the role of reversible ATIII binding in surface anticoagulant activity.

Main Methods:

• Covalent immobilization of albumin-heparin conjugates onto carboxylated polystyrene surfaces.
• Binding studies of ATIII from buffer and plasma solutions.
• Assays to measure thrombin activity and inactivation rates on heparinized surfaces.
• Investigation of protein competition for binding sites.

Main Results:

• Heparinized surfaces bind ATIII reversibly, with higher binding from buffer than plasma.
• Plasma proteins and heparin-binding proteins compete with ATIII for surface sites.
• Surface-bound thrombin activity is reduced at higher ATIII concentrations.
• ATIII effectively inactivates surface-bound thrombin at an accelerated rate compared to solution.
• Formation of Thrombin-Antithrombin III (TAT) complexes, with partial retention on the surface.

Conclusions:

• Reversible ATIII binding to immobilized heparin dictates anticoagulant efficacy.
• Protein competition and adsorption significantly impact ATIII availability on heparinized surfaces.
• Surface-bound thrombin inactivation by ATIII is influenced by heparin's catalytic effect and localized ATIII concentration.