NAD+ research spans mitochondrial metabolism, glycolysis, redox state, sirtuin-dependent signalling, poly-ADP-ribose polymerase activity and cellular stress responses, with the NAD+/NADH ratio widely used as a biochemical marker of cellular redox balance (Learn more). Research applications include energy metabolism, DNA-damage-response signalling and gene regulation, alongside related metabolic and ageing-research compounds such as MOTS-c and SS-31. Because NAD+ is chemically reactive and hygroscopic, batch documentation should be used to confirm the identity and condition of the specific material supplied.
From boiled yeast juice to a Nobel Prize
The NAD+ story begins in London in 1906, when Arthur Harden and William Young were studying how cell-free yeast juice ferments sugar. Passing the juice through a membrane split it into two fractions: a large, heat-sensitive protein portion and a small portion that survived boiling. Neither could ferment glucose on its own, yet mixing them back together restored activity. The small, heat-stable factor was named cozymase.
Working out what cozymase actually was took another two decades. In Stockholm, Hans von Euler-Chelpin purified it and showed it to be a nucleotide containing adenine, nicotinamide, two ribose sugars and two phosphates, and he shared the 1929 Nobel Prize in Chemistry with Harden for their fermentation work. In the mid-1930s Otto Warburg’s laboratory in Berlin traced the chemistry to the nicotinamide ring, the part that picks up hydrogen and hands it on, and identified a phosphorylated sister molecule now called NADP+. Older papers call it diphosphopyridine nucleotide (DPN) or coenzyme I.
Hydride carrier: reading the NAD+/NADH balance
In redox chemistry NAD+ behaves as a shuttle rather than a fuel. Its nicotinamide ring accepts a hydride ion, two electrons and a proton delivered together, to become NADH; when NADH passes that hydride to another enzyme, NAD+ is regenerated intact. Glycolysis relies on this at the glyceraldehyde-3-phosphate dehydrogenase step, the citric acid cycle loads electrons onto NAD+ at three separate dehydrogenases, and complex I of the respiratory chain takes them off again to drive oxygen consumption.
The balance differs sharply from one compartment to another. Classic measurements in freeze-clamped rat liver by Williamson, Lund and Krebs put the free cytoplasmic NAD+/NADH ratio at about 725 in well-fed animals, while the mitochondrial matrix came out in single figures, a far more reduced environment. NADH cannot cross the inner mitochondrial membrane directly, so shuttle systems such as malate–aspartate carry reducing equivalents across instead. The reduced form also gives researchers a convenient handle: NADH absorbs light at 340 nm and fluoresces blue, while NAD+ does neither, so countless dehydrogenase assays and tissue autofluorescence studies simply follow that signal.
Sirtuins and CD38: enzymes that spend NAD+
A second side of NAD+ biology appeared when researchers found enzymes that break the molecule apart instead of borrowing its electrons. In 2000, Shin-ichiro Imai, Leonard Guarente and colleagues reported in Nature that yeast Sir2, a gene-silencing protein linked to yeast lifespan, is an NAD+-dependent histone deacetylase. Mammals carry seven relatives, SIRT1 to SIRT7, spread across the nucleus, cytoplasm and mitochondria. Each strips an acetyl or other acyl group from a lysine on its target protein and cleaves NAD+ in the process, releasing nicotinamide, so sirtuin activity is tied directly to how much NAD+ a cell can spare. Free nicotinamide in turn inhibits sirtuins, a feedback loop experimenters have to allow for.
CD38 is a far hungrier consumer. This membrane enzyme, familiar as an immune-cell marker, hydrolyses NAD+ to nicotinamide and ADP-ribose and also makes cyclic ADP-ribose, a calcium-releasing messenger. In a 2016 Cell Metabolism study from the Mayo Clinic, Camacho-Pereira and colleagues found CD38 levels climbed with age in mouse tissues, while mice lacking CD38 held on to NAD+ and mitochondrial function as they aged, through a mechanism that depended on the mitochondrial sirtuin SIRT3.
Rebuilding the pool: NAMPT salvage and the riboside route
Because sirtuins, PARPs and CD38 keep turning NAD+ into nicotinamide, cells need a quick way to rebuild it. In mammals the main route is salvage. Nicotinamide phosphoribosyltransferase (NAMPT) adds a phosphoribose group to nicotinamide to make nicotinamide mononucleotide (NMN), the rate-limiting step, and NMN adenylyltransferases then attach the adenosine half to complete the cofactor. Three versions, NMNAT1 to NMNAT3, work in the nucleus, the Golgi and cytoplasm, and mitochondria, so each pool is topped up locally. The selective NAMPT inhibitor FK866 drains NAD+ from cultured cells, making it a standard tool for testing which effects truly depend on the cofactor. Cells can also start from nicotinic acid, or build NAD+ from scratch out of tryptophan. Nicotinamide that leaves the loop by methylation is a separate story, told on our 5-Amino-1MQ page.
In 2004 Pawel Bieganowski and Charles Brenner described another entry point: nicotinamide riboside (NR), phosphorylated by NR kinases in a route conserved from yeast to humans, and they identified NR as a nutrient in milk. NR and NMN are now the two precursors most often seen in cell and animal studies. More recently, the 2020 identification of SLC25A51 as the carrier that imports NAD+ into mammalian mitochondria settled a long-running question about how the matrix pool is supplied.
