title: Characterization of an ascorbate peroxidase in plastids of tobacco BY-2 cells.
abstract: In higher plants, ascorbate peroxidase (APX; EC 1.11.1.11), the major H2O2-scavenging enzyme, occurs in several distinct isoenzymes that are localized in cytosol and various cell organelles. Here, we have purified and characterized an APX from the soluble fraction of plastids of non-photosynthetic tobacco BY-2 cells. The plastidic APX was a monomer with a molecular weight of 34 000. The enzymatic properties of the plastidic APX, including the rapid inactivation by H2O2 in ascorbate-depleted medium, were highly comparable with those of the chloroplastic stromal APX of spinach and tea leaves. However, the other chloroplastic APX isoenzyme, the thylakoid-membrane bound APX, was not detected in the plastids of the BY-2 cells. The N-terminal amino acid sequence of the plastidic APX was completely identical with the deduced amino acid sequence of a previously identified cDNA sequence of tobacco chloroplastic APX. When a green fluorescence protein gene tagged with the chloroplast-targeting signal sequence of APX was expressed in the BY-2 cells, the fluorescence protein exclusively localized into plastids, and not into mitochondria. We conclude that plastidic APX in non-photosynthetic tissues is the same as the chloroplastic APX that occurs in leaves.
authors.affiliation: Department of Life Science and Biotechnology, Faculty of Life and Environmental Science, Shimane University, 1060 Nishikawatsu, Matsue 690-8504, Japan United Graduate School of Agricultural Sciences, Tottori University, 4-101 Koyama-Minami, Tottori 680-0945, Japan Department of Food and Nutrition, Faculty of Agriculture, Kinki University, 3327-204 Nakamachi, Nara 631-8505, Japan.
authors.forename: Rapolu
authors.initials: R
authors.lastname: Madhusudhan
authors.forename: Takahiro
authors.initials: T
authors.lastname: Ishikawa
authors.forename: Yoshihiro
authors.initials: Y
authors.lastname: Sawa
authors.forename: Shigeru
authors.initials: S
authors.lastname: Shigeoka
authors.forename: Hitoshi
authors.initials: H
authors.lastname: Shibata