Study on the molecular basis for the regulation of redox metabolism network in plastids

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Autotrophic capacity of plants depends on a series of redox of redox metabolisms. An electron carrir protein, ferredoxin (Fd) and Fd-dependent enzymes function in combination as a molecular machinery for such metabolisms. The process of electron partitioning via Fd to various enzymes within plastids is crucial for photosynthetic activity and elucidation of its molecular mechanism is the main aim of this study. Following results has been obtained.1) X-ray crystsl structure of an electron transfer complex of root Ed and Fd:NADP+ reductase has been determied and this structure is found to be different from that of lesf counterpart.2) Electron transfer between sulfite reductase and Fd was investigate using wild type ans their mutant molecules and redox potential of Fd was found to be important for activity and substrate specificity of sulfite reductase. X-ray crystal analysis of this enzyme is now ongoing.3) Site diredted mutagenesis study of Fd-dependent glutamate synthase was done. Amino acids necessary for the activity of he amidotransferae domain of this enzyme were identified.4) Based on the total total genome information of Arabidopsis, 4 Fd isoprotiens were prepared and purified by reconbinant technique. Their abilities in the electron transfer to photosystem. I, Fd:NADP+ reductase and sulfite reductase were significantly different and physiological differentiation of their role was elucidated. Now proteins which interact with each Fd isoprotein are under investigation.5) A cyanobacterial mutant lacking Fd-dependent glutamate synthase exhibits unbalancing of carbon and nitrogen assimilation probably due to disturbance of partitioning of reducing equivalent. In response to this unbalancing the expression of glutamate synthase gene was up and down-regulated. We could monitor this gene expression by reporterassay syatem.