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Sirtuin
Sirtuin or Sir2 proteins are a class of proteins that possess either mono-ADP-ribosyltransferase, or deacylase activity, including deacetylase, desuccinylase, demalonylase, demyristoylase and depalmitoylase activity. Sirtuins regulate important biological pathways in bacteria, archaea and eukaryotes. The name Sir2 comes from the yeast gene 'silent mating-type information regulation 2', the gene responsible for cellular regulation in yeast.
Sirtuins have been implicated in influencing a wide range of cellular processes like aging, transcription, apoptosis, inflammation and stress resistance, as well as energy efficiency and alertness during low-calorie situations. Sirtuins can also control circadian clocks and mitochondrial biogenesis.
Yeast Sir2 and some, but not all, sirtuins are protein deacetylases. Unlike other known protein deacetylases, which simply hydrolyze acetyl-lysine residues, the sirtuin-mediated deacetylation reaction couples lysine deacetylation to NAD hydrolysis. This hydrolysis yields O-acetyl-ADP-ribose, the deacetylated substrate and nicotinamide, itself an inhibitor of sirtuin activity. The dependence of sirtuins on NAD links their enzymatic activity directly to the energy status of the cell via the cellular NAD:NADH ratio, the absolute levels of NAD, NADH or nicotinamide or a combination of these variables.
== Species distribution ==
Whereas bacteria and archaea encode either one or two sirtuins, eukaryotes encode several sirtuins in their genomes. In yeast, roundworms, and fruitflies, sir2 is the name of the sirtuin-type protein. This research started in 1991 by Leonard Guarente of MIT. Mammals possess seven sirtuins (SIRT1-7) that occupy different subcellular compartments such as the nucleus (SIRT1, -2, -6, -7), cytoplasm (SIRT1 and SIRT2) and the mitochondria (SIRT3, -4 and -5).
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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