Measuring the Kinetics of the Binding of Xenoestrogens and Estrogen Receptor Alpha by Fluorescence Polarization

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• 作者：Kwok-Wing Yiu ; Chi-Kin Lee ; Ka-Cheung Kwok ; Nai-Ho Cheung
• 刊名：Environmental Science & Technology
• 出版年：2014
• 出版时间：October 7, 2014
• 年：2014
• 卷：48
• 期：19
• 页码：11591-11599
• 全文大小：439K
• ISSN：1520-5851

文摘

The mechanism of endocrine disruption by environmental xenoestrogens is unclear. Bisphenol-A (BPA) is an example. Its concentration in human serum is low, and its binding with estrogen receptor (ER) is weak. Yet its effect on prostate and mammary gland development was observed. We investigated whether this effect could be explained in terms of binding kinetics. We used the method of fluorescence polarization anisotropy to measure the kinetic rate constants of the binding of ER伪 with 19 xenoestrogens. Relative binding affinities (RBA) were also deduced from the kinetics. We drew three observations. First, our RBAs were consistent with published values, thus establishing the validity of our results. Second, our method allowed the determination of low RBAs (鈭?0^鈥?) of lipophilic ligands, such as dibutyl phthalate. They could not be measured by steady-state IC₅₀ assays because of their low solubility. Third, we found that BPA had a surprisingly high k_on > 10⁴ M^鈥? s^鈥?. While its RBA was 1500 times lower than that of 17尾 estradiol (E2), its k_on was >1/90 that of E2. As a result, a 10 min surge of BPA from pM to nM could drive the fraction of BPA-activated ER伪 to a potent 0.1%. This might help to explain the observable estrogenic impacts of BPA.