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Articles by Masayuki Fujita
Total Records ( 2 ) for Masayuki Fujita
  M.D. Hossain , Toshisada Suzuki and Masayuki Fujita
  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.
  Pankaj Kumar Bhowmik , Toshiyuki Matsui , Masayuki Fujita , Md. Zakir Hossain and Eizou Miki
  Two inhibitors of the first enzyme phenylalanine ammonia lyase (PAL) in the phenylpropanoid pathway were used to investigate the role of phenolic metabolism in lignification and toughness of Asparagus spears. Spears were soaked for 1 h at 20°C in aqueous solution of α-aminooxi-β-phenylpropionic acid (AOPP) at 0, 100, 300 and 600 μM. Liquid 2,5-Norbornadiene (NBD) was applied with a micropipette onto a sheet of filter paper in a 6.4 liter big jar which was immediately sealed with a cover. Liquid NBD readily volatilized at 25°C in a closed chamber. The amount of liquid applied was calculated to give the desired gaseous concentration (6000 μl L-1) in the jar. Both AOPP and NBD inhibited PAL activity and significantly decreased fiber content in both top and bottom portions of the spears. Northern blot analysis showed that expression in mRNA level coincided well with the changes in PAL activity and fiber content. These results confirm the view that AOPP and NBD, inhibitors of PAL enzyme activity, reduce PAL gene expression and decrease the fiber content of Asparagus spears, suggesting that downstream products of PAL enzyme activity may have a regulatory role in the lignification process.
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