title: Inhibition characteristics of hypericin on rat small intestine glutathione-S-transferases.
abstract: Glutathione-S-transferases constitute a family of enzymes involving in the detoxification of xenobiotics, signalling cascades and serving as ligandins or/and catalyzing the conjugation of various chemicals and drugs. The widely expressed cytosolic GST-pi is a marker protein in various cancers and its increased concentration is linked to drug resistance. GST-pi is autoregulated by S-glutathionylation and it catalyzes the S-glutathionylation of other proteins in response to oxidative or nitrosative stress. S-glutathionylation of GST-pi results in multimer formation and the breakage of ligand binding interactions with c-Jun NH(2)-terminal kinase (JNK). Another widely expressed GST enzyme, GST-alpha is assumed as a marker in hepatocellular damage, is implicated in cancer, asthma, cardiovascular disease and response to chemotherapy. Although, it was shown that hypericin binds and inhibits GST-alpha and GST-pi, the inhibition characteristics have not been investigated in detail. The aim of this study was to investigate the effects of hypericin on major GSTs; GST-alpha and GST-pi purified from rat small intestine. When GSH used as varied substrate the inhibition pattern with hypericin was uncompetitive for GST-alpha (K(i)=0.16 + or - 0.02 microM) and noncompetitive for GST-pi (K(i) = 2.46 + or - 0.43 microM). While using CDNB (1-chloro-2,4-dinitrobenzene) as the varied substrate, the inhibition patterns were noncompetitive for GST-alpha and competitive for GST-pi; K(i) values for GST-alpha and GST-pi were 1.91 + or - 0.21 and 0.55 + or - 0.07 microM, respectively. Since hypericin accumulated in cancer cells and important in photodynamic therapy (PDT), inhibition of GST-alpha and GST-pi by hypericin might increase the effectivity of the treatment. Considering that GST-pi is responsible for the drug resistance its inhibition might increase the benefit obtained from chemotherapy.
authors.affiliation: Department of Biochemistry, Faculty of Medicine, Dokuz Eylul University, Inciralti, 35340, Izmir, Turkey.
authors.forename: Gamze
authors.initials: G
authors.lastname: Tuna
authors.forename: Gulnihal
authors.initials: G
authors.lastname: Kulaksiz Erkmen
authors.forename: Ozlem
authors.initials: O
authors.lastname: Dalmizrak
authors.forename: Arin
authors.initials: A
authors.lastname: Dogan
authors.forename: I Hamdi
authors.initials: IH
authors.lastname: Ogus
authors.forename: Nazmi
authors.initials: N
authors.lastname: Ozer
mesh_terms: D000818:Animals; D000873:Anthracenes; D002853:Chromatography, Liquid; D004591:Electrophoresis, Polyacrylamide Gel; D005982:Glutathione Transferase / Q000378:metabolism*; D007421:Intestine, Small / Q000187:drug effects* / Q000201:enzymology; D007700:Kinetics; D010569:Perylene / Q000031:analogs & derivatives* / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley
chemical_list: D000873:Anthracenes; D010569:Perylene; C004965:hypericin; D005982:Glutathione Transferase