title: Purification of Glutathione S-Transferase pi from Erythrocytes and Evaluation of the Inhibitory Effect of Hypericin.
abstract: Hypericin is a photosensitizer compound used in the photodynamic therapy (PDT). PDT is an alternative cancer treatment strategy whose function is dependent on the photosensitizers accumulating selectively in tumor cells and following visible or infra-red light induced activation lead to the apoptosis/necrosis of the tumor cells via the formation of reactive oxygen species. Thus, the cellular redox balance is essential for the efficacy of PDT. Among the protective enzyme systems glutathione S-transferases (GST, E.C.2.5.1.18) function in detoxification, protection against oxidative stress and intracellular transport of molecules. It is known that isoenzymes of GST and especially GST-pi is increased in cancer cells and it plays very important functions in the development of resistance to anticancer drugs. Since photosensitizers are used intravenously, it is important to elucidate the effects of photosensitizers on the erythrocyte enzymes. The aim of the present study was to investigate the impact of hypericin on human erythrocyte GST-pi (heGST-pi). Purification yield of 71% and purification fold of 2550 were achieved by using conventional chromatographic methods. The specific activity of the enzyme is found as 51 U/mg protein. Hypericin inhibited heGST-pi in a dose dependent manner and inhibition was biphasic. Noncompetitive type of inhibition was observed with both substrates, GSH and CDNB. The inhibitory constant (K i ) values obtained from Lineweaver-Burk, Dixon, secondary plots; slope and y-intercept versus 1/S (substrate) and from non-linear regression analysis were in good correlation: K i (GSH) was calculated as 0.19 ± 0.01 μM and K i (CDNB) as 0.26 ± 0.03 μM.
authors.affiliation: Department of Medical Biochemistry, Faculty of Medicine, Hacettepe University, 06100, Ankara, Turkey.
authors.forename: Seyhan
authors.initials: S
authors.lastname: Turk
authors.affiliation: Department of Medical Biochemistry, Faculty of Medicine, Hacettepe University, 06100, Ankara, Turkey.
authors.forename: Gulnihal
authors.initials: G
authors.lastname: Kulaksiz Erkmen
authors.affiliation: Department of Medical Biochemistry, Faculty of Medicine, Near East University, Nicosia, 99138, Mersin 10, Turkey.
authors.forename: Ozlem
authors.initials: O
authors.lastname: Dalmizrak
authors.affiliation: Department of Medical Biochemistry, Faculty of Medicine, Near East University, Nicosia, 99138, Mersin 10, Turkey.
authors.forename: I Hamdi
authors.initials: IH
authors.lastname: Ogus
authors.affiliation: Department of Medical Biochemistry, Faculty of Medicine, Near East University, Nicosia, 99138, Mersin 10, Turkey. nozertbd@gmail.com.
authors.forename: Nazmi
authors.initials: N
authors.lastname: Ozer
mesh_terms: D000873:Anthracenes; D000970:Antineoplastic Agents / Q000494:pharmacology*; D004912:Erythrocytes / Q000201:enzymology*; D051549:Glutathione S-Transferase pi / Q000037:antagonists & inhibitors* / Q000737:chemistry / Q000302:isolation & purification*; D006801:Humans; D007700:Kinetics; D010569:Perylene / Q000031:analogs & derivatives* / Q000494:pharmacology
chemical_list: D000873:Anthracenes; D000970:Antineoplastic Agents; D010569:Perylene; C004965:hypericin; D051549:Glutathione S-Transferase pi
keywords: GST-pi; Human erythrocyte; Hypericin; Inhibition kinetics