研究领域

Biochemistry

Photosynthesis Biological Electron Transfer Iron-Containing Proteins Plant Nitrogen and Sulfur Metabolism Disulfide-Containing Regulatory Proteins The iron-sulfur protein ferredoxin plays a key role in photosynthesis in all oxygen-evolving organisms. Ferredoxin, which contains a single [2Fe-2S] cluster that functions as a low-potential, one-electron carrier, is reduced in a light-dependent reaction and subsequently serves as the electron donor for a large number of electron-requiring processes. Prof. Knaff’s group studies five enzymes that use reduced ferredoxin as the electron donor: sulfite reductase; nitrate reductase; nitrite reductase; thioredoxin reductase; and glutamate synthase. A major focus of this work is identification of the specific protein domains involved in the interactions between ferredoxin and these enzymes. Kinetic and spectroscopic measurements are also being carried out to elucidate the mechanisms of several of these enzymes and x-ray crystallography is being used to determine three-dimensional structures for nitrite reductase and glutamate synthase. A key step in sulfate assimilation involves the reduction of 5’-adenylsulfate (APS), a reaction catalyzed by the enzyme APS reductase. Prof. Knaff’s group is studying the mechanism of APS reductases, isolated from bacteria, algae and plants, with particular emphasis on the roles of disulfide/dithiol redox couples and of a unique [4Fe-4S] cluster in the enzyme mechanism. X-ray crystallography and NMR spectroscopy are being used in attempts to determine the structures of these enzymes. A possible role for APS reductase in the response of plants to oxidative stress is also being explored. Thioredoxins and glutaredoxins are small ubiquitous proteins that contain a single disulfide in the oxidized form, which is converted to two thiols in the reduced form. Prof. Knaff’s group is studying the role of these proteins in the regulation of enzymatic activity and of gene expression and their role in protecting cells against oxidative damage. Studies of the mechanism of disulfide reduction are also being carried out.

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"The interaction of spinach nitrite reductase with ferredoxin: A site-directed mutation study."M. Hirasawa; J. N. Tripathy; R. Somasundaram; M. K. Johnson; M. Bhalla; J. P. Allen and D. B. Knaff Molecular Plant 2009, 2, 407-415. "New insights into the catalytic cycle of plant nitrite reductase. Electron transfer kinetics and charge storage."P. Sétif; M. Hirasawa; N. Cassan, B; Lagoutte; J. N. Tripathy and D. B. Knaff Biochemistry 2009, 48, 2828-2838. "Oxidation-reduction properties of maize ferredoxin:sulfite oxidoreductase.”Hirasawa, M.; Nakayama, M.; Hase, T.; Knaff, D.B. Biochim. Biophys. Acta 2004, 1608, 140-148. "Complex formation between ferredoxin and Synechococcus ferredoxin:nitrate oxidoreductase.”Hirasawa, M.; Rubio, L.M.; Griffin, J.L.; Flores, E.; Herrero, A.; Li, J.; Kim, S.-K.; Hurley, J.K.; Tollin, G.; Knaff, D.B. Biochim. Biophys. Acta 2004, 1608, 155-162. "The mechanism of spinach chloroplast ferredoxin-dependent nitrite reductase: spectroscopic evidence for intermediate states.”Kuznetsova, S.; Knaff, D.B.; Hirasawa, M.; Lagoutte, B.; Sétif, P. Biochemistry 2004, 43, 510-517. "The effect of pH on the oxidation-reduction properties of thioredoxins.”Setterdahl, A.T.; Chivers, P.T.; Hirasawa, M.; Lemaire, S.D.; Keryer, E.; Miginiac-Maslow, M.; Kim, S.-K.; Mason, J.; Jacquot, J.-P.; Longbine, C.C.; de Lamotte-Guery, F.; Knaff D.B. Biochemistry 2003, 42, 14877-14884.