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J. Biol. Chem., Vol. 279, Issue 25, 25995-26004, June 18, 2004

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Demethoxy-Q, An Intermediate of Coenzyme Q Biosynthesis, Fails to Support Respiration in Saccharomyces cerevisiae and Lacks Antioxidant Activity^*

Sergio Padilla, Tanya Jonassen, María A. Jiménez-Hidalgo, Daniel José M. Fernández-Ayala, Guillermo López-Lluch, Beth Marbois, Plácido Navas, Catherine F. Clarke, and Carlos Santos-Ocaña¶

From the Centro Andaluz de Biología del Desarrollo, Universidad Pablo de Olavide, 41013-Sevilla, Spain and Department of Chemistry and Biochemistry, University of California, Los Angeles, 607 Charles E. Young Drive East, Los Angeles, California, 90095-1569

Caenorhabditis elegans clk-1 mutants cannot produce coenzyme Q₉ and instead accumulate demethoxy-Q₉ (DMQ₉). DMQ₉ has been proposed to be responsible for the extended lifespan of clk-1 mutants, theoretically through its enhanced antioxidant properties and its decreased function in respiratory chain electron transport. In the present study, we assess the functional roles of DMQ₆ in the yeast Saccharomyces cerevisiae. Three mutations designed to mirror the clk-1 mutations of C. elegans were introduced into COQ7, the yeast homologue of clk-1: E233K, predicted to disrupt the di-iron carboxylate site considered essential for hydroxylase activity; L237Stop, a deletion of 36 amino acid residues from the carboxyl terminus; and P175Stop, a deletion of the carboxyl-terminal half of Coq7p. Growth on glycerol, quinone content, respiratory function, and response to oxidative stress were analyzed in each of the coq7 mutant strains. Yeast strains lacking Q₆ and producing solely DMQ were respiratory deficient and unable to support ⁶either NADH-cytochrome c reductase or succinate-cytochrome c reductase activities. DMQ₆ failed to protect cells against oxidative stress generated by H₂O₂ or linolenic acid. Thus, in the yeast model system, DMQ does not support respiratory activity and fails to act as an effective antioxidant. These results suggest that the life span extension observed in the C. elegans clk-1 mutants cannot be attributed to the presence of DMQ per se.

Received for publication, January 1, 2004 , and in revised form, April 2, 2004.

^* This work was supported by National Institutes of Health Grant GM45952, NIA, National Institutes of Health Grant AG19777, and Spanish Ministry of Education and Science Grant BMC2002-01602. 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.

^¶ To whom correspondence should be addressed: Centro Andaluz de Biología del Desarrollo, Universidad Pablo de Olavide, Carretera de Utrera km 1, 41013-Sevilla, Spain. Tel.: 954-34-9093; Fax: 954-34-9376; E-mail: csantos{at}dex.upo.es.

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