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J. Biol. Chem., Vol. 281, Issue 46, 34803-34809, November 17, 2006

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The Inhibition of Mitochondrial Complex I (NADH:Ubiquinone Oxidoreductase) by Zn^2+*

From the Medical Research Council (MRC) Dunn Human Nutrition Unit, Wellcome Trust/MRC Building, Hills Road, Cambridge, CB2 2XY, United Kingdom

NADH:ubiquinone oxidoreductase (complex I) from bovine heart mitochondria is a highly complicated, membrane-bound enzyme. It is central to energy transduction, an important source of cellular reactive oxygen species, and its dysfunction is implicated in neurodegenerative and muscular diseases and in aging. Here, we describe the effects of Zn²⁺ on complex I to define whether complex I may contribute to mediating the pathological effects of zinc in states such as ischemia and to determine how Zn²⁺ can be used to probe the mechanism of complex I. Zn²⁺ inhibits complex I more strongly than Mg²⁺, Ca²⁺, Ba²⁺, and Mn²⁺ to Cu²⁺ or Cd²⁺. It does not inhibit NADH oxidation or intramolecular electron transfer, so it probably inhibits either proton transfer to bound quinone or proton translocation. Thus, zinc represents a new class of complex I inhibitor clearly distinct from the many ubiquinone site inhibitors. No evidence for increased superoxide production by zinc-inhibited complex I was detected. Zinc binding to complex I is mechanistically complicated. During catalysis, zinc binds slowly and progressively, but it binds rapidly and tightly to the resting state(s) of the enzyme. Reactivation of the inhibited enzyme upon the addition of EDTA is slow, and inhibition is only partially reversible. The IC₅₀ value for the Zn²⁺ inhibition of complex I is high (10–50 µM, depending on the enzyme state); therefore, complex I is unlikely to be a major site for zinc inhibition of the electron transport chain. However, the slow response of complex I to a change in Zn²⁺ concentration may enhance any physiological consequences.

Received for publication, August 3, 2006 , and in revised form, August 31, 2006.

^* This work was supported by The Medical Research Council. 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 To whom correspondence should be addressed: MRC Dunn Human Nutrition Unit, Wellcome Trust/MRC Bldg., Hills Rd., Cambridge, CB2 2XY, UK. Tel.: 44-1223-252810; Fax: 44-1223-252815; E-mail: jh{at}mrc-dunn.cam.ac.uk.

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