The sirtuins are a family of nicotinamide adenine dinucleotide (NAD þ )-dependent protein deacetylases that regulate cell survival, metabolism, and longevity. Humans have seven sirtuins (SIRT1-SIRT7) with distinct subcellular locations and functions. SIRT3 is localized to the mitochondrial matrix and its expression is selectively activated during fasting and calorie restriction. Activated SIRT3 deacetylates several key metabolic enzymes-acetyl-coenzyme A synthetase, long-chain acylcoenzyme A

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... yl-CoA) dehydrogenase (LCAD), and 3-hydroxy-3-methylglutaryl CoA synthase 2-and enhances their enzymatic activity. Disruption of SIRT3 activity in mice, either by genetic ablation or during high-fat feeding, is associated with accelerated development of metabolic abnormalities similar to the metabolic syndrome in humans. SIRT3 is therefore emerging as a metabolic sensor that responds to change in the energy status of the cell and modulates the activity of key metabolic enzymes via protein deacetylation.