Journal Article

Characterization of Ascorbate Peroxidases from Unicellular Red Alga <i>Galdieria partita</i>

Satoshi Sano, Masami Ueda, Sakihito Kitajima, Toru Takeda, Shigeru Shigeoka, Norihide Kurano, Shigetoh Miyachi, Chikahiro Miyake and Akiho Yokota

in Plant and Cell Physiology

Published on behalf of Japanese Society of Plant Physiologists

Volume 42, issue 4, pages 433-440
Published in print April 2001 | ISSN: 0032-0781
Published online April 2001 | e-ISSN: 1471-9053 | DOI: http://dx.doi.org/10.1093/pcp/pce054
Characterization of Ascorbate Peroxidases from Unicellular Red
Alga Galdieria
partita

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Galdieria partita, a unicellular red alga isolated from acidic hot springs and tolerant to sulfur dioxide, has at least two ascorbate peroxidase (APX) isozymes. This was the first report to demonstrate that two isozymes of APX are found in algal cells. Two isozymes were separated from each other at the hydrophobic chromatography step of purification and named APX-A and APX-B after the elution order in the chromatography. APX-B accounted for 85% of the total activity. Both isozymes were purified. APXs from Galdieria were monomers whose molecular weights were about 28,000, similar to stromal APX of higher plants. APX-A cross-reacted with monoclonal antibody raised against APX of Euglena gracilis in immunoblotting, but APX-B did not, although the antibody can recognize all other APXs tested. The amino-terminal sequences of APX-A and -B from Galdieria had some homology with each other but little homology with those from other sources. Their Km values for ascorbate and hydrogen peroxide were comparable with those of APX from higher plants. Unlike the green algal enzymes, the donor specificities of Galdieria APXs were as high as those of plant chloroplastic APX. On the contrary, these APXs reduced tertiary-butyl hydroperoxide as an electron acceptor as APXs from Euglena and freshwater Chlamydomonas do. The inhibition of APX-A and -B by cyanide and azide, and characteristics of their light absorbance spectra indicated that they were heme peroxidases.

Keywords: Key words: Ascorbate peroxidase — Galdieria partita — Hydrogen peroxide — Isozyme — Red alga.; Abbreviations: AsA, ascorbate; APX, ascorbate peroxidase; PVDF, polyvinyliden difluoride; SOD, superoxide dismutase.

Journal Article.  5688 words.  Illustrated.

Subjects: Biochemistry ; Molecular and Cell Biology ; Plant Sciences and Forestry

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