Sirtuins are protein deacetylases with multiple isoforms active in the nucleus, cytosol and mitochondria all serving unique functions and requiring NAD+. These sirtuins function to condense chromatin and yet  protein abundance has less to do with potency than does the availability of NAD+ which can be synthesized from multiple routes. Furthermore, SIRT1 has been associated with  antagonizing age-related decreases in the amplitudes of the SCN output obtaining age-linked differentiating  phases of increases and decreases observed within a circadian cycle..

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