Fuel for the sirtuins

The sirtuins, SIRT1 to SIRT7, are enzymes that tune genes and mitochondria to the energy state of the cell. Each time a sirtuin works, it burns one molecule of NAD+. SIRT1 in the nucleus and SIRT3 in the mitochondria switch on fat burning, mitochondrial building and stress defence. When NAD+ falls, the sirtuins go quiet, and the cell behaves older.