Antithrombin BM from human plasma: an antithrombin binding moderately to heparin

Area of Science:

• Biochemistry
• Hematology
• Protein Chemistry

Background:

• Human blood contains multiple antithrombin factors.
• Antithrombin III is a well-characterized thrombin inhibitor.
• The existence and properties of other antithrombins are less understood.

Purpose of the Study:

• To purify and characterize a novel human antithrombin, designated Antithrombin BM (AT BM).
• To compare the properties of AT BM with Antithrombin III (AT III).
• To determine the contribution of AT BM to overall antithrombin activity in human blood.

Main Methods:

• Purification of AT BM from Cohn fraction IV.
• Polyacrylamide gel electrophoresis for molecular weight determination.
• Heparin binding assays and antithrombin activity measurements.
• Comparison of inhibitory specificity and immunological cross-reactivity with AT III.

Main Results:

• AT BM was purified approximately 60-fold, showing a single band of ~70,000 molecular weight.
• AT BM exhibits moderate heparin binding, requiring higher heparin concentrations for activity compared to AT III.
• AT BM is dependent on heparin(oids) for activity, shows specificity for thrombin, and lacks cross-reactivity with anti-AT III antibodies.
• AT BM may account for up to 40% of the total antithrombin activity in human blood.

Conclusions:

• Antithrombin BM is a distinct human antithrombin with unique biochemical and functional properties.
• AT BM's properties differ significantly from AT III, including heparin binding affinity and specificity.
• AT BM represents a substantial component of antithrombin activity in human plasma, suggesting a significant physiological role.