@article{oai:repo.qst.go.jp:00044939,
 author = {Akiyama, Nobuko and Nakanishi, Ikuo and Ohkubo, Kei and Fukuzumi, Shunichi and Ozawa, Toshihiko and et.al and 中西 郁夫 and 小澤 俊彦},
 issue = {1},
 journal = {Journal of Biochemistry},
 month = {Jul},
 note = {N-beta-Alanyl-5-S-glutathionyl-3,4-dihydroxyphenylalanine (5-S-GAD), an insect-induced antibacterial peptide, generates hydrogen peroxyde (H2O2) that exerts antitumour activity.  We have investigated the precise mechanism of H2O2 production from 5-S-GAD by autoxidation aiming to understand its action toward tumour cells.  Using the electron spin resonance (ESR) technique, we detected a strong signal due to radical formation from 5-S-GAD.  Surprisingly, the ESR signal of the radicalo derived from 5-S-GAD appeared after incubation for 30 min at 310 K in the buffer at pH 7.4; the signal was persistently detected for 10 h in the absence of catalytic metal ions.  The computer simulation of the observed ESR spectrum together with the theoretical calculation of the spin density of the radical species indicates that an o-semiquinone radical anion was formed from 5-S-GAD.  We demonstrated that H2O2 is produced via the formation of superoxide anion by the electron-transfer reduction of molecular oxygen by the 5-S-GAD anion, which is in equiliblium with 5-S-GAD in the aqueous solution.  The radical formation and the subsequent H2O2 production were inhibited by superoxide dismutase (SOD), when the antitumour activity of 5-S-GAD was inhibited by SOD.  Thus, the formation of the o-semiquinone radical anion would be necessary for the antitumour activity of 5-S-GAD as an intermediate in the production of cytotoxic H2O2.},
 pages = {41--48},
 title = {A Long-Lived o-Semiquinone Radical Anion is Formed from N-beta-alanyl-5-S-glutathionyl-3,4-dihydroxyphenylalanine (5-S-GAD), an Insect-derived Antibacterial Substance},
 volume = {142},
 year = {2007}
}