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Enzyme kinetics and substrate selectivities of rat glutathione S-transferase isoenzymes towards a series of new 2-substituted 1-chloro-4-nitrobenzenes

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Author: Aar, E.M. van der · Buikema, D. · Commandeur, J.N.M. · Koppele, J.M. te · Ommen, B. van · Bladeren, P.J. van · Vermeulen, N.P.E.
Type:article
Date:1996
Institution: Leiden/Amsterdam Ctr. for Drug Res., Department of Pharmacochemistry, Vrije Universiteit, De Boelelaan 1083, 1081 HV, Amsterdam, Netherlands TNO Preventie en Gezondheid TNO Voeding
Source:Xenobiotica, 2, 26, 143-155
Identifier: 233289
Keywords: Nutrition · glutathione transferase · isoenzyme · nitrobenzene derivative · animal tissue · article · controlled study · enzyme kinetics · enzyme specificity · glutathione metabolism · nonhuman · rat · Animals · Chromatography, Affinity · Dinitrochlorobenzene · Glutathione Transferase · Isoenzymes · Kidney · Kinetics · Liver · Rats · Spectrophotometry, Ultraviolet · Substrate Specificity · Animalia · Felis catus

Abstract

1. Four different rat glutathione S-transferase (GST) isoenzymes, belonging to three different classes, were examined for their GSH conjugating capacity towards 11 2-substituted 1-chloro-4-nitrobenzene derivatives. Significant differences were found in their enzyme kinetic parameters K(m), k(cat) and k(cat)/K(m). 2. Substrates with bulky substituents on the ortho-position appeared to have high affinities (low K(m)'s) for the active site of the GST-isoenzymes, suggesting that there is sufficient space in this area of the active site. A remarkably high K(m) (low affinity) was found for 2-chloro-5-nitropyridine towards all GST-isoenzymes examined. 3. GST 3-3 catalysed the reaction between GSH and the substrates most efficiently (high k(cat)) compared with the other GST-isoenzymes. Moreover, GST 3-3 showed clear substrate selectivities towards the substrates with a trifluoromethyl-, chlorine- and bromine-substituent. 1-Chloro-2,4-dinitrobenzene and 2-chloro-5-nitrobenzonitrile were most efficiently conjugated by all four GST-isoenzymes examined. 4. When the rate of the conjugation reactions was followed, a linear increase of formation of GS-conjugate could be seen for 2-chloro-5-nitrobenzonitrile during a much longer period of time than for 1-chloro-2,4-dinitrobenzene with all GST-isoenzymes examined. Therefore, it is suggested that 2-chloro-5-nitrobenzonitrile might be recommended as an alternative model substrate in GST-research. Chemicals/CAS: Dinitrochlorobenzene, 97-00-7; Glutathione Transferase, EC 2.5.1.18; Isoenzymes