| Summary: | This work investigates the reactions of proteins with ROS when mitochondria are exposed to H<sub>2</sub>O<sub>2</sub> or when they generate ROS endogenously. Using isolated mitochondria, those proteins that are particularly sensitive to low concentrations of H<sub>2</sub>O<sub>2</sub> and to ROS generated by the mitochondrial electron transport chain were first identified using a method called Redox-Difference Gel Electrophoresis (Redox-DIGE). Most redox sensitive thiol proteins identified by Redox-DIGE were involved either in fatty acid oxidation or in the regulation of the pyruvate dehydrogenase complex. Next the mechanisms by which ROS selectively oxidise mitochondrial thiol proteins were investigated; it was determined that H<sub>2</sub>O<sub>2</sub> generated by the electron transport chain may either oxidise mitochondrial thiol proteins directly or indirectly, through oxidation of the peroxiredoxin and thioredoxin redox couples. To determine if ROS generated by mitochondria might act as a redox signal by altering the functions of mitochondrial proteins, the effect of protein thiol oxidation was tested on the activity of two proteins: pyruvate dehydrogenase kinase and propionyl-CoA carboxylase. Loss of pyruvate dehydrogenase kinase and propionyl-CoA carboxylase activity correlated with protein thiol oxidation and was very sensitive to ROS, suggesting a plausible mechanism of redox regulation of these proteins <i>in vivo. </i>Lastly, glutathionylation of complex I was investigated in intact mitochondria exposed to a glutathione oxidant; two cysteine residues on the 75 kDa subunit of complex I were shown to become glutathionylated. The functional effect of glutathionylation of these two cysteine residues on complex I activity is currently under investigation.
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