The Role of Photosynthetic Electron Transport in the Oxidative Degradation of Chloroplastic Glutamine Synthetase1
AUTOR(ES)
Palatnik, Javier F.
FONTE
American Society of Plant Physiologists
RESUMO
The stability of chloroplastic glutamine synthetase (GS; EC 6.3.1.2) was investigated under photooxidative stress using wheat (Triticum aestivum L.) leaves, chloroplasts, and chloroplast lysates. Illuminated seedlings sprayed with the superoxide radical (O2⨪) propagator methyl viologen showed rapid GS decline dependent on MV concentration and exposure time. Degradation products of approximately 39 and 31 kD were detected when chloroplast lysates containing both stroma and thylakoids were illuminated in the presence of MV or H2O2. In all cases, GS cleavage was prevented by the addition of the electron transport inhibitor 3-(3,4-dichlorophenyl)-1,1-dimethylurea. Full protection against degradation could also be obtained by the incorporation of chelators or antioxidant enzymes. Maximal rates of degradation required the presence of transition metals and reducing compounds such as NADPH or dithiothreitol. Similar patterns of GS cleavage were obtained when seedlings were exposed to high doses of irradiation. The results indicate that chloroplastic GS is extremely prone to oxidative cleavage, and that reduced transition metals, presumably resulting from the destruction of iron-sulfur clusters by light-generated O2⨪, play a crucial role in the degradation process. The physiological implications of GS lability to oxidative stress are discussed.
ACESSO AO ARTIGO
http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=59409Documentos Relacionados
- Chloroplastic glutamine synthetase from Brassica napus.
- Photoresponses in Rhodobacter sphaeroides: role of photosynthetic electron transport.
- The Role of Plastocyanin in the Adjustment of the Photosynthetic Electron Transport to the Carbon Metabolism in Tobacco1
- Electron Transport Controls Glutamine Synthetase Activity in the Facultative Heterotrophic Cyanobacterium Synechocystis sp. PCC 6803.
- Oxidative inactivation of glutamine synthetase subunits.