Phosphorylation of Mitochondrial Elongation Factor Tu in Ischemic Myocardium

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.