Author contributions: J.M., T.L., A.W., P.B., B.O?R, and G.W.H. designed research; J.M., T.L., A.W., and P.B. performed research; J.M., T.L., A.W., P.B., B.O?R, and G.W.H. analyzed data; J.M., B.O?R, and G.W.H. wrote the manuscript; all authors edited the paper.

Background: Mitochondrial protein O-GlcNAcylation is not well understood.

Results: Eighty-eight mitochondrial proteins, involved in diverse pathways, are O-GlcNAcylated; and an overall increased O-GlcNAcylation leads to altered mitochondrial function.

Conclusion: O-GlcNAcylation is on many mitochondrial proteins within the oxidative phosphorylation system, modulating cardiac mitochondrial function.

Significance: O-GlcNAc cycles on many proteins within mitochondria, leading to altered function.