Research projects of Dr. Ohnishi's laboratory focus on structure/function studies of the NADH-quinone oxidoreductase (also known as complex I) in both prokaryotic and eukaryotic systems. This is the largest and important enzyme which contains 8 or 9 iron-sulfur clusters, one non-covalently bound FMN, and 2 protein-bound quinone species. The laboratory's major interest is to examine the molecular mechanism of the coupling between electron and proton transfer in this enzyme. Very recently this laboratory published a novel conformation-driven semiquinone-gated proton pumping mechanism as listed below (ref. 1).

As basic techniques in the laboratory, electron paramagnetic resonance, optical spectroscopies and redox potentiometry are used. Extensive collaborations are conducted with other laboratories having expertise in molecular biology or other spectroscopic techniques such as electron nuclear double resonance (ENDOR), electron spin-echo (ESE), as well as Fourier transform infrared (FTIR) spectroscopies.

The Ohnishi lab is also studying medically relevant reactive oxygen and nitric oxide radicals in the NADH-quinone oxidoreductase reactions, using spin-trapping techniques.

RECENT REPRESENTATIVE PUBLICATIONS:

1. Ohnishi, T and J.C. Salerno. (2005) Conformation-driven and semiquinone-gated proton-pump mechanism in the NADH-ubiquinone oxidoreductase (complex I). FEBS Letters 579:4555-4561.
2. Ohnishi, S.T., T. Ohnishi, S. Muranaka, H. Fujita, H. Kimura, H. Uemura, K. Yoshida, and K. Utsumi (2005) A possible site of superoxide generation in the complex I segment of rat heart mitochondria. J . Bioenerg. Biomembr. 37:1-15.
3. Nakamaru-Ogiso, E., T. Yano, T. Yagi, and T. Ohnishi (2005) Characterization of the iron-sulfur cluster N7 (N1c) in the Subunit NuoG of the proton-translocating NADH-quinone oxidoreductase from Escherichia coli. J. Biol. Chem. 280:301-307.
4. Ohnishi, T., J.J. Johnson, T. Yano, R. LoBrutto, W.R. Widger. (2005) Thermodynamic and EPR studies of slow relaxing SQ species in the isolated bovine heart complex I. FEBS Letters 579:500-506.
5. Yano, T., W. R. Dunham, and T. Ohnishi (2005) Characterization of the ∆μ_H⁺-sensitive SQ species (SQ_Nf) and the interaction with cluster N2: New insight into the energy-coupled electron transfer in complex I. Biochemistry 44:1744-1754.
6. Magnitsky, S., L. Toulokhonova, T. Yano, V.D. Sled, C. Hägerhäll, V.G. Grivennikova, D.S. Burbaev, A.D. Vinogradov and T. Ohnishi (2002) EPR characterization of ubisemiquinones and iron-sulfur cluster N2, central components of the energy coupling in the NADH-ubiquinone oxidoreductase (somplex I) in situ. J. Bioenerg. Biomembr. 34:193-208.
7. Ohnishi, T., C.C. Moser, C.P. Page, P.L. Dutton, T. Yano (2000) Simple redox-linked proton-transfer design: New insights from structures of quinol-fumarate reductase. Structure with Folding and Design. 8:R23-32.
8. Ohnishi, T. (1998) Iron-sulfur clusters/semiquinones in complex I. Biochim. Biophys. Acta    1364:186-206.
9. Ohnishi, T. and Salerno, J.C. (1982) Fe-S complexes in the mitochondrial electron transport chain. In Iron-Sulfur Proteins, Vol. IV (T.G. Spiro, ed.) Wiley Publishing Co., Inc., New York, pp. 285-327.