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Updated: Jul 14, 2026

Detecting the Ligand-binding Domain Dimerization Activity of Estrogen Receptor Alpha Using the Mammalian Two-Hybrid Assay
Published on: December 19, 2018
Modeling binding equilibrium in a competitive estrogen receptor binding assay.
Jung-Hwan Kwon1, Lynn E Katz, Howard M Liljestrand
1Department of Civil, Architectural and Environmental Engineering, The University of Texas at Austin, 1 University Station C1786, Austin, TX 78712-0273, USA.
Free concentration, not nominal, is a superior dose-metric for competitive binding assays. This study demonstrates its independence from receptor concentration, crucial for endocrine disruptor research.
Area of Science:
- Environmental Chemistry
- Toxicology
- Biochemistry
Background:
- Free concentration is critical for receptor-mediated toxicants but rarely used as a dose-metric.
- Endocrine disrupting compounds (EDCs) like DES, EE2, and BPA pose environmental and health risks.
Purpose of the Study:
- To evaluate the relative binding affinity of DES, EE2, and BPA to human estrogen receptor alpha.
- To compare the efficacy of free concentration versus nominal concentration as a dose-metric in competitive binding assays.
Main Methods:
- Competitive Enzyme-Linked Immunosorbent Assay (ELISA) using human estrogen receptor alpha.
- Measurement of available receptors and dissociation constant for 17beta-estradiol.
- Generation of binding inhibition curves using both free and nominal concentrations as dose-metrics.
Main Results:
- Binding inhibition curves differed significantly between free and nominal concentrations, especially for strongly binding ligands.
- The ratio of IC50 values (relative to DES) was influenced by assay conditions when using nominal concentration.
- Estimates using free concentration were independent of receptor concentration, unlike those using nominal concentration.
Conclusions:
- Free concentration is a more robust and reliable dose-metric for competitive binding assays than nominal concentration.
- This finding has significant implications for accurately assessing the toxicological impact of endocrine disrupting compounds.
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