Estrogen sulfotransferase (EST) catalyzes the transfer of the sulfuryl group from 3'-phosphoadenosine 5'-phosphosulfate (PAPS) to 17beta-estradiol (E2). The sulfation of E2 prevents it from binding to, and thereby activating, the estrogen receptor. The regulation of EST appears to be causally linked to tumorigenesis in the breast and endometrium. In this study, recombinant human EST is characterized, and the catalytic mechanism of the transfer reaction is investigated in ligand binding and initial rate experiments. The native enzyme is a dimer of 35-kDa subunits. The apparent equilibrium constant for transfer to E2 is (4.5 +/- 0.2) x 10(3) at pH 6.3 and T = 25 +/- 2 degrees C. Initial rate studies provide the kinetic constants for the reaction and suggest a sequential mechanism. E2 is a partial substrate inhibitor (Ki = 80 +/- 5 nM). The binding of two E2 per EST subunit suggests that the partial inhibition occurs through binding at an allosteric site. In addition to providing the dissociation constants for the ligand-enzyme complexes, binding studies demonstrate that each substrate binds independently to the enzyme and that both the E.PAP.E2S and E.PAP.E2 dead-end complexes form. These results strongly suggest a Random Bi Bi mechanism with two dead-end complexes.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
customersupport@researchsolutions.com
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
This site is protected by reCAPTCHA and the Google Privacy Policy and Terms of Service apply.
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.