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Updated: Jun 9, 2026

Bio-layer Interferometry for Measuring Kinetics of Protein-protein Interactions and Allosteric Ligand Effects
Published on: February 18, 2014
Evidence of the E*-E equilibrium from rapid kinetics of Na+ binding to activated protein C and factor Xa
Austin D Vogt1, Alaji Bah, Enrico Di Cera
1Department of Biochemistry and Molecular Biology, Saint Louis University School of Medicine, St. Louis, Missouri 63104, USA.
Abstract:
Na(+) binding to thrombin enhances the procoagulant and prothrombotic functions of the enzyme and obeys a mechanism that produces two kinetic phases: one fast (in the microsecond time scale) due to Na(+) binding to the low activity form E to produce the high activity form E:Na(+) and another considerably slower (in the millisecond time scale) that reflects a pre-equilibrium between E and the inactive form E*. In this study, we demonstrate that this mechanism also exists in other Na(+)-activated clotting proteases like factor Xa and activated protein C. These findings, along with recent structural data, suggest that the E*-E equilibrium is a general feature of the trypsin fold.
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