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Biological Chemistry

Editor-in-Chief: Brüne, Bernhard

Editorial Board Member: Buchner, Johannes / Ludwig, Stephan / Sies, Helmut / Turk, Boris / Wittinghofer, Alfred

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S-Glucuronidation of 7-mercapto-4-methylcoumarin by human UDP glycosyltransferases in genetically engineered fission yeast cells

Daniela Buchheit1 / Ellen I. Schmitt1 / Daniel Bischoff2 / Thomas Ebner2 / 1

1PomBioTech GmbH, Campus Geb. A1, D-66123 Saarbrücken, Germany

2Boehringer Ingelheim Pharma GmbH and Co. KG, Drug Metabolism and Pharmacokinetics, D-88400 Biberach an der Riß, Germany

Corresponding author

Citation Information: Biological Chemistry. Volume 392, Issue 12, Pages 1089–1095, ISSN (Online) 1437-4315, ISSN (Print) 1431-6730, DOI: 10.1515/BC.2011.194, December 2011

Publication History

Received:
2011-08-03
Accepted:
2011-08-23

Abstract

Human UDP glycosyltransferases (UGTs) play an important role in xenobiotic detoxification. They increase the solubility of their substrates by adding a sugar moiety (such as glucuronic acid) to different functional entities (such as hydroxyl groups). The aim of this study was to investigate how glucuronidation of a standard substrate is affected by a change of the hetero­atom at the conjugation site. For this purpose, we compared the in vitro glucuronidation rates of 4-methylumbelliferone and 7-mercapto-4-methylcoumarin, respectively. Human liver microsomes catalyzed the S-glucuronidation of 7-mercapto-4-­methylcoumarin almost as efficient as the O-glucuronidation of 4-methylumbelliferone. When testing isoenzyme specificity by whole cell biotransformation with fission yeast strains that recombinantly express all 19 human members of the UGT1 and UGT2 families, it was found that 13 isoenzymes were able to glucuronidate 7-mercapto-4-methylcoumarin, with five of them being specific for this substrate and the other eight also converting 4-methylumbelliferone under these conditions. The remaining six UGTs did not accept either substrate. Out of the eight isoenzymes that glucuronidated both substrates, four catalyzed both reactions approximately to the same extent, while three displayed higher conversion rates towards 4-methylumbelliferone and one preferred 7-mercapto-4-methylcoumarin. These data suggest that 7-mercapto-4-methylcoumarin is a convenient new standard substrate for monitoring S-glucuronidation.

Keywords: coumarin; fission yeast; S-glucuronide; thiol; UGT; whole cell biotransformation

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