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J. Biol. Chem., Vol. 282, Issue 33, 24407-24415, August 17, 2007

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Catalase Takes Part in Rat Liver Mitochondria Oxidative Stress Defense^*

Mauro Salvi, Valentina Battaglia, Anna Maria Brunati, Nicoletta La Rocca, Elena Tibaldi, Paola Pietrangeli^¶, Lucia Marcocci^¶, Bruno Mondovì^¶, Carlo A. Rossi, and Antonio Toninello¹

From the Dipartimento di Chimica Biologica, Università di Padova, Viale G. Colombo 3, 35121 Padova, the Dipartimento di Biologia, Università di Padova, Viale G. Colombo 3, 35131 Padova, and the ^¶Dipartimento di Scienze Biochimiche, A. Rossi Fanelli, Università di Roma "La Sapienza," P. le A. Moro 5, 00185 Roma, Italy

Highly purified rat liver mitochondria (RLM) when exposed to tert-butylhydroperoxide undergo matrix swelling, membrane potential collapse, and oxidation of glutathione and pyridine nucleotides, all events attributable to the induction of mitochondrial permeability transition. Instead, RLM, if treated with the same or higher amounts of H₂O₂ or tyramine, are insensitive or only partially sensitive, respectively, to mitochondrial permeability transition. In addition, the block of respiration by antimycin A added to RLM respiring in state 4 conditions, or the addition of H₂O₂, results in O₂ generation, which is blocked by the catalase inhibitors aminotriazole or KCN. In this regard, H₂O₂ decomposition yields molecular oxygen in a 2:1 stoichiometry, consistent with a catalatic mechanism with a rate constant of 0.0346 s^-1. The rate of H₂O₂ consumption is not influenced by respiratory substrates, succinate or glutamate-malate, nor by N-ethylmaleimide, suggesting that cytochrome c oxidase and the glutathione-glutathione peroxidase system are not significantly involved in this process. Instead, H₂O₂ consumption is considerably inhibited by KCN or aminotriazole, indicating activity by a hemoprotein. All these observations are compatible with the presence of endogenous heme-containing catalase with an activity of 825 ± 15 units, which contributes to mitochondrial protection against endogenous or exogenous H₂O₂. Mitochondrial catalase in liver most probably represents regulatory control of bioenergetic metabolism, but it may also be proposed for new therapeutic strategies against liver diseases. The constitutive presence of catalase inside mitochondria is demonstrated by several methodological approaches as follows: biochemical fractionating, proteinase K sensitivity, and immunogold electron microscopy on isolated RLM and whole rat liver tissue.

Received for publication, February 22, 2007 , and in revised form, April 24, 2007.

^* 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: Dipartimento di Chimica Biologica, Università di Padova, Istituto di Neuroscienze del CNR, Viale G. Colombo 3, 35121 Padova, Italy. Tel.: 39-0498276134; Fax: 39-0498276133; E-mail: antonio.toninello{at}unipd.it.

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