Analysis of acetylation stoichiometry suggests that SIRT 3 repairs nonenzymatic acetylation lesions

Acetylation is frequently detected on mitochondrial enzymes, and the sirtuin deacetylase SIRT 3 is thought to regulate metabolism by deacetylating mitochondrial proteins. However, the stoichiometry of acetylation has not been studied and is important for understanding whether SIRT 3 regulates or suppresses acetylation. Using quantitative mass spectrometry, we measured acetylation stoichiometry in mouse liver tissue and found that SIRT 3 suppressed acetylation to a very low stoichiometry at its target sites. By examining acetylation changes in the liver, heart, brain, and brown adipose tissue of fasted mice, we found that SIRT 3‐targeted sites were mostly unaffected by fasting, a dietary manipulation that is thought to regulate metabolism through SIRT 3‐dependent deacetylation. Globally increased mitochondrial acetylation in fasted liver tissue, higher stoichiometry at mitochondrial acetylation sites, and greater sensitivity of SIRT 3‐targeted sites to chemical acetylation in vitro and fasting‐induced acetylation in vivo , suggest a nonenzymatic mechanism of acetylation. Our data indicate that most mitochondrial acetylation occurs as a low‐level nonenzymatic protein lesion and that SIRT 3 functions as a protein repair factor that removes acetylation lesions from lysine residues.