Allen, Michael D. , Kropat, Janette , Page, M. Dudley , Long, Joanne C. , Merchant, Sabeeha S. .
An inducible MnSOD localizes to the chloroplast and can replace FeSOD during iron-deficiency.
Organisms face a variety of stresses when growing in the natural environment. Photosynthetic organisms face high levels of reactive oxygen species, such as superoxide anion and singlet oxygen, which are generated by the photosynthetic apparatus. These compounds can react with nearby proteins or lipids causing a variety of cellular damage. Organisms counteract the production of superoxide with the superoxide dismutase (SOD) enzyme. This protein catalyzes the disproportionation of superoxide to molecular oxygen and hydrogen peroxide. Hydrogen peroxide is further detoxified by an oxidation / reduction pathway utilizing glutathione and NADPH as electron donors. SOD enzymes contain a variety of cofactors such as Cu / Zn, Ni, Mn, and Fe. Each isoform typically localizes to a particular organelle, in general, Cu / Zn-SOD is a cytosolic enzyme, MnSOD is mitochondrial, and FeSOD is plastid localized. Chlamydomonas reinhardtii lacks a Cu / Zn-SOD but codes for a single FeSOD and five MnSODs. Using cellular fractionation coupled with SOD activity assays and immunoblot analysis, we have localized the major MnSOD isoform to the chloroplast in addition to FeSOD. Interestingly, we note the appearance of an iron-deficiency inducible MnSOD activity that also localizes to the chloroplast. This activity is also induced during manganese deficiency as well as treatment with hydrogen peroxide and the activity profile matches the expression of the MSD3 gene. We conclude that the MSD3 gene product is a functional substitute for FeSOD, which is lost during iron-deficiency.
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1 - University of California, Los Angeles, Chemistry and Biochemistry, 607 Charles E. Young Dr., Los Angeles, CA, 90095, USA
2 - University of California, Los Angeles, Chemistry and Biochemistry
Presentation Type: Plant Biology Abstract
Location: Exhibit Hall (Northeast, Southwest & Southeast)/Hilton
Date: Sunday, July 8th, 2007
Time: 8:00 AM