Sirtuin (silent mating type information regulation 2 homolog) 5 (S. cerevisiae), also known as SIRT5 is a protein which in humans in encoded by the SIRT5 gene and in other species by the Sirt5 gene.

This gene encodes a member of the sirtuin family of proteins, homologs to the yeast Sir2 protein. Members of the sirtuin family are characterized by a sirtuin core domain and grouped into four classes. The functions of human sirtuins have not yet been determined; however, yeast sirtuin proteins are known to regulate epigenetic gene silencing and suppress recombination of rDNA. Studies suggest that the human sirtuins may function as intracellular regulatory proteins with mono-ADP-ribosyltransferase activity. The protein encoded by this gene is included in class III of the sirtuin family. Alternative splicing of this gene results in multiple transcript variants. [provided by RefSeq, Jul 2010].
Function: NAD-dependent protein deacetylase that activates CPS1 and contributes to the regulation of blood ammonia levels during prolonged fasting. Deacetylates CPS1 and increases CPS1 activity in response to elevated NAD levels during fasting (By similarity). Can deacetylate cytochrome c and a number of other proteins (in vitro).