NAD-dependent deacetylase sirtuin-3, mitochondrial, also known as SIRT3, belongs to the sirtuin family of proteins. Members of the sirtuin family are characterized by a sirtuin core domain and grouped into four classes. The functions of human sirtuins have a range of molecular functions and have emerged as important proteins in aging, stress resistance and metabolic regulation. SIRT3 exhibits NAD+-dependent deacetylase activity in the mitochondria. Over-expression of SIRT3 results in increased levels of the mitochondrial uncoupling protein 1. SIRT3 protein levels are also elevated in certain breast cancers. Recombinant human SIRT3 protein, fused to Histag at N-terminus, was expressed in E.coli and purified by using conventional chromatography techniques.