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Asian Journal of Plant Sciences
Year: 2006  |  Volume: 5  |  Issue: 2  |  Page No.: 345 - 352

Inhibitory Substances to Glutathione S-Transferases in Pumpkin Seedlings

M.D. Hossain, Toshisada Suzuki and Masayuki Fujita    

Abstract: Endogenous substrates and physiological ligands of Glutathione s-transferases (GSTs) have capabilities to reduce the enzyme reactions for xenobiotic substrates. In order to investigate the physiological counterparts to plant GSTs, the inhibitory effect of pumpkin (Cucurbita maxima Duch.) seedling extract on 1-chloro-2,4-dinitrobenzene (CDNB) conjugating activities of pumpkin GSTs was examined. Alcoholic extract of pumpkin seedlings showed different degrees of inhibitory effect for the three GST species namely, CmGSTU1, CmGSTU2 and CmGSTU3. In the assay system, 50% inhibition of CmGSTU1 and CmGSTU3 activities were achieved with the extracts from 178 and 96 mg fresh tissues, respectively. The activity of CmGSTU2 was decreased marginally by the extract and did not reach 50% level. To separate into constituents, the extract was applied to Sep-pac Vac C18 column and eluted with different concentrations of methanol. Inhibitory potencies of Methanol-Eluted Fractions (MEFs) against CmGSTU3 were estimated. Twenty, forty and sixty percent MEFs exhibited higher inhibitions followed by 0% MEF. CmGSTU3 activity was decreased marginally by 100% MEF. MEFs of pumpkin seedlings extract were successively analyzed by HPLC. The analyses indicated that MEFs contain a number of inhibitors with different degrees of hydrophobicity, while 0% MEF also contains hydrophilic inhibitors. The above results suggest that pumpkin seedlings contain various physiological substrates or ligands for pumpkin GSTs.

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