US EPA

2510782 

Journal Article 

Measuring the kinetics of the binding of xenoestrogens and estrogen receptor alpha by fluorescence polarization 

Yiu, KW; Lee, CK; Kwok, KC; Cheung, NH 

2014 

1 

Environmental Science & Technology
ISSN: 0013-936X
EISSN: 1520-5851 

48 

19 

11591-11599 

English 

25180905 

10.1021/es503801c 

WOS:000343016600072 

https://search.proquest.com/docview/2000211970?accountid=171501
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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 ERα 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 (∼10(-4)) 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 kon > 10(4) M(-1) s(-1). While its RBA was 1500 times lower than that of 17β estradiol (E2), its kon 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 ERα to a potent 0.1%. This might help to explain the observable estrogenic impacts of BPA. 

article; binding capacity; bisphenol A; blood serum; dibutyl phthalate; estradiol; estrogen receptors; fluorescence; inhibitory concentration 50; ligands; mammary development; solubility; xenoestrogens