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J. Biol. Chem., Vol. 281, Issue 4, 2061-2070, January 27, 2006

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Protein Kinase A-mediated Phosphorylation Modulates Cytochrome c Oxidase Function and Augments Hypoxia and Myocardial Ischemia-related Injury^*

From the Department of Animal Biology, School of Veterinary Medicine, University of Pennsylvania, Philadelphia, Pennsylvania 19104

We have investigated the effects of hypoxia and myocardial ischemia/reperfusion on the structure and function of cytochrome c oxidase (CcO). Hypoxia (0.1% O₂ for 10 h) and cAMP-mediated inhibition of CcO activity were accompanied by hyperphosphorylation of subunits I, IVi1, and Vb and markedly increased reactive O₂ species production by the enzyme complex in an in vitro system that uses reduced cytochrome c as an electron donor. Both subunit phosphorylation and enzyme activity were effectively reversed by 50 nM H89 or 50 nM myristoylated peptide inhibitor (MPI), specific inhibitors of protein kinase A, but not by inhibitors of protein kinase C. In rabbit hearts subjected to global and focal ischemia, CcO activity was inhibited in a time-dependent manner and was accompanied by hyperphosphorylation as in hypoxia. Additionally, CcO activity and subunit phosphorylation in the ischemic heart were nearly completely reversed by H89 or MPI added to the perfusion medium. Hyperphosphorylation of subunits I, IVi1, and Vb was accompanied by reduced subunit contents of the immunoprecipitated CcO complex. Most interestingly, both H89 and MPI added to the perfusion medium dramatically reduced the ischemia/reperfusion injury to the myocardial tissue. Our results pointed to an exciting possibility of using CcO activity modulators for controlling myocardial injury associated with ischemia and oxidative stress conditions.

Received for publication, July 18, 2005 , and in revised form, November 4, 2005.

^* This work was supported in part by National Institutes of Health Grant GM-49683 (to N. G. A.) and an American Heart Association grant (to J. F. S.). 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 On sabbatical leave from the Department of Biochemistry, Faculty of Medicine and Health Sciences, United Arab Emirates University, Al Ain, United Arab Emirates.

² To whom correspondence should be addressed: Dept. of Animal Biology, School of Veterinary Medicine, University of Pennsylvania, 3800 Spruce St., Philadelphia, PA 19104. Tel.: 215-898-8819; Fax: 215-573-6651; E-mail: narayan{at}vet.upenn.edu.

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