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J. Biol. Chem., Vol. 281, Issue 32, 23013-23017, August 11, 2006

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The Redox-Bohr Group Associated with Iron-Sulfur Cluster N2 of Complex I^*

From the Universität Frankfurt, Zentrum der Biologischen Chemie, Molekulare Bioenergetik, D-60590 Frankfurt am Main, Germany

Proton pumping respiratory complex I (NADH:ubiquinone oxidoreductase) is a major component of the oxidative phosphorylation system in mitochondria and many bacteria. In mammalian cells it provides 40% of the proton motive force needed to make ATP. Defects in this giant and most complicated membrane-bound enzyme cause numerous human disorders. Yet the mechanism of complex I is still elusive. A group exhibiting redox-linked protonation that is associated with iron-sulfur cluster N2 of complex I has been proposed to act as a central component of the proton pumping machinery. Here we show that a histidine in the 49-kDa subunit that resides near iron-sulfur cluster N2 confers this redox-Bohr effect. Mutating this residue to methionine in complex I from Yarrowia lipolytica resulted in a marked shift of the redox midpoint potential of iron-sulfur cluster N2 to the negative and abolished the redox-Bohr effect. However, the mutation did not significantly affect the catalytic activity of complex I and protons were pumped with an unchanged stoichiometry of 4 H⁺/2e^-. This finding has significant implications on the discussion about possible proton pumping mechanism for complex I.

Received for publication, April 11, 2006 , and in revised form, June 2, 2006.

^* This work was supported by the Deutsche Forschungsgemeinschaft SFB472, Project P2 and the Center for Membrane Proteomics of the University of Frankfurt. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

¹ These authors contributed equally to this work.

² To whom correspondence should be addressed: Universität Frankfurt, Zentrum der Biologischen Chemie, Molekulare Bioenergetik, Theodor-Stern-Kai 7, Haus 26, D-60590 Frankfurt am Main, Germany. Tel.: 49-69-6301-6926; Fax: 49-69-6301-6970; E-mail: brandt{at}zbc.kgu.de.

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				M. A. Tocilescu, U. Fendel, K. Zwicker, S. Kerscher, and U. Brandt Exploring the Ubiquinone Binding Cavity of Respiratory Complex I J. Biol. Chem., October 5, 2007; 282(40): 29514 - 29520. [Abstract] [Full Text] [PDF]