351. Stable complex formation between serine protease inhibitor and zymogen: coagulation factor X cleaves the Arg393-Ser394 bond in a reactive centre loop of antithrombin in the presence of heparin.
- Author
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Nakatomi Y, Tsuji M, Gokudan S, Hanada-Dateki T, Nakashima T, Miyazaki H, Hamamoto T, Nakagaki T, and Tomokiyo K
- Subjects
- Antithrombins pharmacology, Arginine chemistry, Arginine metabolism, Enzyme Precursors antagonists & inhibitors, Enzyme Precursors metabolism, Factor X antagonists & inhibitors, Factor X chemistry, Heparin metabolism, Humans, Serine chemistry, Serine metabolism, Serine Proteinase Inhibitors pharmacology, Structure-Activity Relationship, Antithrombins chemistry, Enzyme Precursors chemistry, Factor X metabolism, Heparin pharmacology, Serine Proteinase Inhibitors chemistry
- Abstract
Antithrombin (AT) inhibits several blood coagulation proteases, including activated factor X (FXa), by forming stable complexes with these proteases. Herein, we demonstrate that AT forms a stable complex with zymogen factor X (FX). Sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) and size-exclusion chromatography analyses showed that AT and FX formed an SDS-stable complex, which is distinct in apparent molecular mass from an FXa-AT complex, in the presence of heparin. Amino-terminal sequence analysis of the complex following SDS-PAGE under reducing conditions provided clear evidence that AT forms this complex with the heavy chain of FX, because two sequences, HGSPVDI (residues 1-7 of AT) and SVAQATS (residues 1-7 of the heavy chain of FX), were identified. Furthermore, sequence SLNPNRV, which corresponds to residues 394-400 of AT, was identified in the non-reduced FX-AT complex, indicating that FX cleaved the Arg393-Ser394 bond in a reactive centre loop of AT. Unfractionated heparin induced FX-AT complex formation more effectively than low-molecular weight heparin or AT-binding pentasaccharide, and appeared to promote complex formation mainly via a template effect. These data suggest that AT is capable of forming a stable complex with zymogen FX by acting as an inhibitor in the presence of heparin.
- Published
- 2012
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