| Budget Amount *help |
¥3,830,000 (Direct Cost: ¥3,500,000、Indirect Cost: ¥330,000)
Fiscal Year 2007: ¥1,430,000 (Direct Cost: ¥1,100,000、Indirect Cost: ¥330,000)
Fiscal Year 2006: ¥2,400,000 (Direct Cost: ¥2,400,000)
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| Research Abstract |
γ-Glutamyltransferase (GGT) catalyzes the hydrolysis and transpeptidation of the γ-glutamyl moiety of γ-glutamyl peptides such as glutathione. We found the followings in this study.
(1) Subcellular fractionation of radish (Raphanus sativus) cotyledon and isolation of vacuole revealed that soluble GGT is a vacuolar enzyme. Acivicin, a GGT inhibitor, mediated the in vivo catabolism inhibition of the glutathione S-conjugate generated from endogenous glutathione and exogenously supplied monochlorobimane. Thus, soluble GGT is possibly involved in the catabolism of glutathione and glutathione S-conjugates.
(2) Tobacco plants transformed with□□ radish full-length cDNAs (RsGGT1, RsGGT2 and RsGGT3) encoding putative heterodimeric GGT isoforms. Expression analysis indicated that RsGGTs showed different organ expression patterns. The overexpression of RsGGT1 and RsGGT2cDNAs, but not that of RsGGT3cDNA, resulted in an increase of NaCl-extractable bound GGT activity in transgenic tobacco plants. These results suggest that RsGGT1 and RsGGT2cDNAs encode heterodimeric bound GGT isoforms.
(3) Arabidopsis mutants harboring T-DNA or transposon insertions in putative GGT genes AtGGT1, AtGGT2 and AtGGT3 were characterized. Gene expression analysis indicated that the identified atggt1-1, atggt2-1, atggt2-2 and atggt3-1 plants were GGT-null mutants. GGT activity analysis indicated that the atggt1 mutant allele was deficient in cell wall bound GGT, whereas the two atggt2 mutant alleles and the atggt3 mutant allele were deficient in soluble GGT. GSH contents and GSH catabolic rates in wild type and atggt1 plants suggest that AtGGT1 is involved in GSH catabolism. AtGGT1, 2, 3 seem to be corresponding to RsGGT-1, 2, 3. based on their sequences. However there still be discrepancy between these genes.
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