Nicotinamide adenine dinucleotide is transported into mammalian mitochondria. Author Antonio Davila, Ling Liu, Karthikeyani Chellappa, Philip Redpath, Eiko Nakamaru-Ogiso, Lauren Paolella, Zhigang Zhang, Marie Migaud, Joshua Rabinowitz, Joseph Baur Publication Year 2018 Type Journal Article Abstract Mitochondrial NAD levels influence fuel selection, circadian rhythms, and cell survival under stress. It has alternately been argued that NAD in mammalian mitochondria arises from import of cytosolic nicotinamide (NAM), nicotinamide mononucleotide (NMN), or NAD itself. We provide evidence that murine and human mitochondria take up intact NAD. Isolated mitochondria preparations cannot make NAD from NAM, and while NAD is synthesized from NMN, it does not localize to the mitochondrial matrix or effectively support oxidative phosphorylation. Treating cells with nicotinamide riboside that is isotopically labeled on the nicotinamide and ribose moieties results in the appearance of doubly labeled NAD within mitochondria. Analogous experiments with doubly labeled nicotinic acid riboside (labeling cytosolic NAD without labeling NMN) demonstrate that NAD(H) is the imported species. Our results challenge the long-held view that the mitochondrial inner membrane is impermeable to pyridine nucleotides and suggest the existence of an unrecognized mammalian NAD (or NADH) transporter. Keywords Animals, Mice, Biological Transport, Humans, Cell Line, Mice, Inbred C57BL, Male, HEK293 Cells, NAD, Niacinamide, HL-60 Cells, Mitochondria, Liver, Mitochondria, Muscle, Myoblasts, Nicotinamide Mononucleotide, Pyridinium Compounds Journal Elife Volume 7 Date Published 2018 Jun 12 ISSN Number 2050-084X DOI 10.7554/eLife.33246 Alternate Journal Elife PMCID PMC6013257 PMID 29893687 PubMedPubMed CentralGoogle ScholarBibTeXEndNote X3 XML