The different forms of antithrombin II in serum

Area of Science:

• Biochemistry
• Hematology

Background:

• Antithrombin III (AT III) is a key regulator of coagulation.
• Understanding the forms and complexes of AT III in serum is crucial for hemostasis research.

Purpose of the Study:

• To isolate and characterize antithrombin III (AT III) complexes from human serum.
• To investigate the molecular weight and potential polymeric nature of AT III complexes in vivo.

Main Methods:

• Affinity chromatography using heparin-agarose.
• Gel filtration chromatography.
• Radioactive labeling with 125I-thrombin to detect thrombin-AT III complexes.

Main Results:

• Complexed AT III bound less strongly to heparin-agarose than free AT III, with approximately 50% of AT III found free.
• A 2.5 x 10(5) molecular weight complex containing thrombin was isolated from serum.
• A 9 x 10(4) molecular weight complex was detected only in synthetic systems, not in serum, suggesting polymeric forms in vivo.
• An AT III antigen, potentially a degradation product, was also isolated.

Conclusions:

• Human serum contains AT III complexes, likely in a polymeric form.
• Further purification revealed a significant thrombin-AT III complex.
• The presence of free AT III and a distinct AT III antigen suggests ongoing AT III turnover or degradation.