Biosensor reveals multiple sources for mitochondrial NAD +

A fluorescent sensor for NAD + in living cells Roles of cellular nicotinamide adenine dinucleotide (NAD + ) in metabolism, aging, and disease have garnered much interest, but methods have been lacking to measure the amounts of NAD + in living cells. Cambronne et al. developed a genetically encoded biosensor that can be used to monitor concentrations of free NAD + in various compartments of a cell (see the Perspective by Guarente). Such concentrations of NAD + appear to be important in regulating the activity of NAD + -consuming enzymes such as sirtuins and ADP-ribosyltransferases. The authors used the sensor to demonstrate that NAD + concentrations in mitochondria of cultured human cells can be controlled by multiple mechanisms. Science , this issue p. 1474 ; see also p. 1396