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(Circulation Research. 2001;89:461.)
© 2001 American Heart Association, Inc.

Molecular Medicine

Phosphorylation of Mitochondrial Elongation Factor Tu in Ischemic Myocardium

Basis for Chloramphenicol-Mediated Cardioprotection

Huaping He, Min Chen, N. Karoline Scheffler, Bradford W. Gibson, Linda L. Spremulli, Roberta A. Gottlieb

From The Scripps Research Institute (H.H., M.C., R.A.G.), La Jolla, Calif; the Department of Chemistry and Pharmaceutical Chemistry (N.K.S., B.W.G.), University of California San Francisco, San Francisco, Calif; and the Department of Chemistry (L.L.S.), University of North Carolina, Chapel Hill, NC.

Correspondence to Roberta A. Gottlieb, MD, Department of Molecular & Experimental Medicine, MEM220, The Scripps Research Institute, 10550 N Torrey Pines Rd, La Jolla, CA 92037. E-mail robbieg{at}scripps.edu

The objective of this study was to identify the mitochondrial proteins that undergo changes in phosphorylation during global ischemia and reperfusion in the isolated rabbit heart. We also assessed whether the cardioprotective intervention of ischemic preconditioning affected mitochondrial protein phosphorylation. We established a reconstituted system using isolated mitochondria and cytosol from control or ischemic hearts. We found that phosphorylation of a 46-kDa protein on a serine residue was increased in ischemia and that phosphorylation was reduced in control or preconditioned hearts. Using 2D gel electrophoresis and mass spectrometry, we have identified the 46-kDa protein as mitochondrial translational elongation factor Tu (EF-Tu_mt). These data reveal that ischemia and preconditioning modulate the phosphorylation of EF-Tu_mt and suggest that the mitochondrial protein synthesis machinery may be regulated by phosphorylation. Phosphorylation of mitochondrial EF-Tu has not been previously described; however, in prokaryotes, EF-Tu phosphorylation inhibits protein translation. We hypothesized that phosphorylation of mitochondrial EF-Tu would inhibit mitochondrial protein translation and attempted to reproduce the effect with inhibition of mitochondrial protein synthesis by chloramphenicol. We found that chloramphenicol pretreatment significantly reduced infarct size, suggesting that mitochondrial protein synthesis is one determinant of myocardial injury during ischemia and reperfusion.

Key Words: ischemia • preconditioning • mitochondria • phosphorylation • chloramphenicol

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