 Recent proteomics experiments reveal that another protein modification, lysine acetylation, is more common in non-histone proteins than has been recognized. There are no data, to our knowledge, regarding a relationship between insulin resistance in vivo in human muscle and protein acetylation. We have used proteomics techniques to discover a number of lysine acetylation sites in skeletal muscle proteins in vivo in humans, and this is prominent in mitochondrial proteins. Preliminary data show that mitochondrial protein acetylation is regulated by muscle contraction, and that this response is reduced in insulin resistance. Finally, the mitochondrial inner membrane protein adenine nucleotide translocase ANT1 was abundantly acetylated under resting conditions, and its deacetylation in response to contraction was reduced in insulin resistance. Because ANT1 exerts significant physiological control strength for ADPATP exchange, and because mitochondrial function is altered in insulin resistance, it is important to characterize this abnormality. Therefore, in order to determine how abnormalities in regulation of lysine acetylation characterize insulin resistant muscle, we propose: 