Phosphorylation of mitochondrial elongation factor tu in ischemic myocardium - Basis for chloramphenicol-mediated cardioprotection

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 ph osphorylation. We established a reconstituted system using isolated mitocho ndria and cytosol from control or ischemic hearts. We found that phosphoryl ation of a 46-kDa protein on a serine residue was increased in ischemia and that phosphorylation was reduced in control or preconditioned hearts. Usin g 2D gel electrophoresis and mass spectrometry, we have identified the 46-k Da protein as mitochondrial translational elongation factor Tu (EF-Tu(mt)). These data reveal that ischemia and preconditioning modulate the phosphory lation of EF-Tu(mt) and suggest that the mitochondrial protein synthesis ma chinery may be regulated by phosphorylation. Phosphorylation of mitochondri al EF-Tu has not been previously described; however, in prokaryotes, EF-Tu phosphorylation inhibits protein translation. We hypothesized that phosphor ylation of mitochondrial EF-Tu would inhibit mitochondrial protein translat ion and attempted to reproduce the effect with inhibition of mitochondrial protein synthesis by chloramphenicol. We found that chloramphenicol pretrea tment significantly reduced infarct size, suggesting that mitochondrial pro tein synthesis is one determinant of myocardial injury during ischemia and reperfusion.