Inhibition of human glutathione S-transferase P1-1 by the flavonoid quercetin.
In the present study, the inhibition of human glutathione S-transferase P1-1 (GSTP1-1) by the flavonoid quercetin has been investigated. The results show a time- and concentration-dependent inhibition of GSTP1-1 by quercetin. GSTP1-1 activity is completely inhibited upon 1 h incubation with 100 microM quercetin or 2 h incubation with 25 microM quercetin, whereas 1 and 10 microM quercetin inhibit GSTP1-1 activity to a significant extent reaching a maximum of 25 and 42% inhibition respectively after 2 h. Co-incubation with tyrosinase greatly enhances the rate of inactivation, whereas co-incubation with ascorbic acid or glutathione prevents this inhibition. Addition of glutathione upon complete inactivation of GSTP1-1 partially restores the activity. Inhibition studies with the GSTP1-1 mutants C47S, C101S and the double mutant C47S/C101S showed that cysteine 47 is the key residue in the interaction between quercetin and GSTP1-1. HPLC and LC-MS analysis of trypsin digested GSTP1-1 inhibited by quercetin did not show formation of a covalent bond between Cys 47 residue of the peptide fragment 45-54 and quercetin. It was demonstrated that the inability to detect the covalent quercetin-peptide adduct using LC-MS is due to the reversible nature of the adduct-formation in combination with rapid and preferential dimerization of the peptide fragment once liberated from the protein. Nevertheless, the results of the present study indicate that quinone-type oxidation products of quercetin likely act as specific active site inhibitors of GSTP1-1 by binding to cysteine 47.
van Zanden
Jelmer J
JJ
Division of Toxicology, Wageningen University, Tuinlaan 5, 6703 HE Wageningen, The Netherlands. jelmer.vanzanden@wur.nl
Ben Hamman
Omar
O
van Iersel
Marlou L P S
ML
Boeren
Sjef
S
Cnubben
Nicole H P
NH
Lo Bello
Mario
M
Vervoort
Jacques
J
van Bladeren
Peter J
PJ
Rietjens
Ivonne M C M
IM
D002851:Chromatography, High Pressure Liquid; D004305:Dose-Response Relationship, Drug; D005982:Glutathione Transferase / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism; D006801:Humans; D013058:Mass Spectrometry; D015394:Molecular Structure; D014442:Monophenol Monooxygenase / Q000378:metabolism; D009154:Mutation; D011794:Quercetin / Q000493:pharmacokinetics / Q000494:pharmacology*
D011794:Quercetin; D014442:Monophenol Monooxygenase; D005982:Glutathione Transferase