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Kinetics and Molecular Interactions in the Rapid Disulfation of Raloxifene (RAL) by Human Sulfotransferase (SULT) 1E1
Author(s) -
Cook Ian Thomas,
Kadlubar Susan Nowell,
Falany Charles Napoleon
Publication year - 2009
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.23.1_supplement.750.8
Subject(s) - sulfation , chemistry , benzothiophene , sulfate , sulfatase , sulfotransferase , stereochemistry , glucuronidation , hydrolysis , metabolism , kinetics , catalysis , biochemistry , enzyme , organic chemistry , microsome , physics , quantum mechanics , thiophene
Sulfation is an important Phase 2 conjugation reaction in the metabolism of steroidal compounds and related therapeutic drugs. RAL is sulfated by several human SULTs to form a monosulfate; however only SULT1E1 forms RAL disulfate (RAL‐diS). Kinetic analysis shows that formation of RAL‐diS is favored at low physiological concentrations of RAL, whereas at higher concentrations RAL monosulfate formation is increased. To better understand RAL sulfation, the benzothiophene‐ and phenolic‐monosulfates were synthesized and used in the kinetic analysis of RAL‐diS formation by SULT1E1. The conversion of RAL‐phenyl‐sulfate to RAL‐diS has a significantly lower Km and greater Kcat than determined with the benzothiophene‐sulfate. Molecular modeling of the two RAL‐monosulfates in the SULT1E1 active site indicates that the binding free energy and orientation of RAL‐phenyl‐sulfate in the active site is more conducive to catalysis than that of the benzothophene‐sulfate. These data indicate that at nanomolar concentrations RAL is preferentially converted to the phenyl‐sulfate then to the disulfate by SULT1E1. Since the RAL phenyl‐sulfate is resistant to hydrolysis by steroid sulfatase this represents a mechanism for the inactivation of RAL by SULT1E1 in breast and endometrial tissues.