Poster: Oxidative Stress

Abs # 128: Analysis of a physiological role of dehydroascorbic acid using yeasts as a model organisms

Presenter:	Amako, Katsumi , amakok@nutr.kobegakuin.ac.jp
Authors	Amako, Katsumi  (A) (B)  Yoshinori, Murata  (C)   Yukiko, Ohnishi  (A)   Yuzo, Yamauchi  (A)   Yukako, Ogiri  (A)   Ritsuko, Kishimoto  (A)   Kiyoshi, Goda  (A) (B)
Affiliations:	(A): Fac. Nutr., Kobe Gakuin University (B): High Tech. Res. Center, Kobe Gakuin University (C): National Inst. Adv. Indust. Sci. Technol.

Yeast has C5 analogue of ascorbic acid, erythroascorbic acid (eAsA), and it has been reported as an antioxidant. The biosynthetic pathway of eAsA in yeast is quite similar of AsA in plants, so we are using yeasts as a model of plant cells in terms of AsA metabolism. Here, we studied about the effect of redox state of eAsA on defence systems against reactive oxygen species in yeasts. Complementary DNA encoding either dehydroascorbate reductase (DHAR) from rice or ascorbate oxidase (ASO) from tobacco on a constitutive expression vector pFL61 are introduced to S. Cerevisiae YPH250 to express these translation products at cytosol. Accumulation of these products was ensured either by enzyme activity assay or by immunoblotting. Yeasts expressing DHAR showed increased sensitivity to hydrogen peroxide and accumulated oxidants, whereas yeasts expressing ASO was resistant to hydrogen peroxide and less oxidants content. Intracellular concentrations of total glutathione was correlated to the resistance of cells against hydrogen peroxide, which strongly suggests that eAsA itself does not play as a gbulkh antioxidant, but a regulator for metabolism of the other antioxidant(s) including glutathione. However, yeast activator protein 1-dependent responses against hydrogen peroxide were physiologically stored irrespective of both amount and redox state of intracellular eAsA. Genes showing the modulation of expression correlating the redox state of eAsA were screened, and their common transacting factor(s) were assumed.