[Report] Biosensor reveals multiple sources for mitochondrial NAD+

Nicotinamide adenine dinucleotide (NAD+) is an essential substrate for sirtuins and poly(adenosine diphosphate–ribose) polymerases (PARPs), which are NAD+-consuming enzymes localized in the nucleus, cytosol, and mitochondria. Fluctuations in NAD+ concentrations within these subcellular compartments are thought to regulate the activity of NAD+-consuming enzymes; however, the challenge in measuring compartmentalized NAD+ in cells has precluded direct evidence for this type of regulation. We desc