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Zinc inhibition of bovine phenol sulfotransferase (bSULT1A1)
Author(s) -
Lapham David E.,
Beckmann Joe D.
Publication year - 2008
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.22.1_supplement.792.3
Subject(s) - zinc , chemistry , sulfation , enzyme , glutathione , titration , biochemistry , isothermal titration calorimetry , titration curve , sulfotransferase , non competitive inhibition , stereochemistry , inorganic chemistry , organic chemistry
Sulfotransferases (SULTs) catalyze sulfate transfer from 3'‐phosphoadenosine‐5'‐phosphosulfate (PAPS) to various acceptors such as phenols and steroids. Zinc is known to inactivate SULTs; however, the mechanism of this inhibition is unknown. We investigated this question using purified recombinant bovine enzyme (bSULT1A1), which reacts broadly with phenolic substrates. Enzyme activities were determined by continuous recording of fluorescence decay during 7‐hydroxycoumarin sulfation. Greatest inhibition was achieved by addition of zinc prior to the substrates, suggesting formation of a SULT:zinc complex. Inhibition is partially reversed upon addition of 2‐mercaptoethanol or glutathione. Zinc dose‐response curves revealed IC 50 values of approximately 9 μM at pH 7.4, compared to 270 μM at pH 5.5. The zinc pH inhibition curve suggests the involvement of a titratable group of pKa ≈ 6.5. Detailed initial velocity analysis with varied PAPS and zinc concentrations indicated zinc to be a non‐competitive inhibitor with a K i = 13.6 μM. Isothermal calorimetric titrations with zinc were adequately fit with a one‐site model and yielded a K d of 2.47 μM with a stoichiometery of 2 metals per bSULT1A1 subunit at pH 7.4. The sensitivity of bSULT1A1 to zinc inhibition, and the reversibility of the inhibition by glutathione, raise questions regarding the role of this metal in regulating sulfation of hormones and drugs.