NAD+ vs NADH
Research Comparison

Research Overview

NAD+ is the oxidized form; NADH is the reduced form. Both are nicotinamide adenine dinucleotide, and together they form a redox pair that serves as the cofactor for many dehydrogenases. NAD+ also has a second job: poly(ADP-ribose) polymerases (PARPs), sirtuins and glycohydrolases such as CD38 use it up as a substrate, apart from its role as an electron carrier (Wilhelm and Hirrlinger, 2012).

So is NADH the same as NAD? No. They are one coenzyme in two redox states, and labs handle them as different reagents. Every NAD+ vs NADH difference traces to one change on the nicotinamide ring, which shifts absorbance, stability in solution and the enzymes that will accept each form. Disguised Alpha supplies NAD+ as buffered lyophilized vials (500MG and 1000MG) and a 200MG/ML liquid, and the precursor NMN as 500MG capsules, for laboratory research use only. NADH is not listed as a single compound.

Structure and Class

Both are pyridine nucleotides, not peptides: an adenosine and a nicotinamide riboside joined through a diphosphate bridge. NAD+ is C21H27N7O14P2, 663.43 g/mol, as on the product page; PubChem CID 5892 gives the same formula at 663.4 g/mol. NADH is C21H29N7O14P2, 665.4 g/mol (PubChem CID 439153).

Reduction adds a hydride, two electrons and a proton, at carbon 4 of the nicotinamide ring, turning the aromatic, positively charged pyridinium of NAD+ into the uncharged 1,4-dihydropyridine of NADH. The ring is where oxidized vs reduced NAD differ, and it is what assays read: both forms absorb near 260 nm through the adenine, but only NADH absorbs at 340 nm (Wolfe et al., 2024).

In 85 independent determinations with a coupled hexokinase and glucose-6-phosphate dehydrogenase method, the molar absorptivity of NADH at 340 nm averaged 6,317 L/mol/cm at 25°C and pH 7.8, a value that shifts with pH, buffer and temperature (McComb et al., 1976).

Side by Side

Research Context: NAD+

NAD+ is the electron acceptor of central carbon metabolism. In glycolysis, glyceraldehyde-3-phosphate dehydrogenase reduces it to NADH; in mitochondria, the pyruvate dehydrogenase complex and three TCA cycle dehydrogenases do the same (Wilhelm and Hirrlinger, 2012).

The consuming enzymes need the oxidized form. With Sir2 enzymes tested in vitro, reducing the nicotinamide ring, as in NADH, was one of the two changes that caused the steepest losses in binding and reactivity. NADH inhibited them only weakly, at an average IC50 of 17 mM, and the authors suggested that shifting the NAD+:NADH ratio without changing NAD+ would barely alter Sir2 activity (Schmidt et al., 2004).

The pattern held for PARP and NADase activity in rat liver fractions: nuclear poly(ADP-ribose) synthetase and a microsomal NAD glycohydrolase used NAD+ and NADP+, but NADH and NADPH were substrates for neither (McCreanor and Bender, 1983).

Research Context: NADH

NADH is the electron donor. In the cytosol, lactate dehydrogenase can reoxidize it by reducing pyruvate to lactate; in mitochondria, complex I of the electron transport chain accepts its electrons and regenerates NAD+. With the Peredox biosensor in cultured and primary cells, glycolysis opposed the lactate dehydrogenase equilibrium and produced a reduced cytosolic NADH-NAD+ state, and primary mouse astrocytes and neurons differed (Hung et al., 2011).

When the electron transport chain declines, the NAD+/NADH ratio falls. In human cells, targeting a water-forming NADH oxidase from Lactobacillus brevis (LbNOX) to the cytosol or mitochondria raised the ratio there, revealed key metabolic fluxes that depend on it, and relieved proliferative and metabolic defects caused by an impaired chain (Titov et al., 2016).

Much of the NADH in a cell is not free. In freeze-clamped rat liver, free NAD+/NADH ratios calculated from dehydrogenase substrate pairs were about 725 in the cytoplasm and about 8 in mitochondria of well-fed rats; both fell with starvation, but the two did not always move together. Free ratios differed greatly from total measurements because much more NADH than NAD+ is protein-bound (Williamson et al., 1967).

Choosing Between Them for a Research Question

The NAD vs NADH choice follows from what the experiment measures. As reagents, NAD+ is the cosubstrate for sirtuin, PARP and NADase assays and the acceptor for dehydrogenase reactions run in the oxidative direction, read as rising absorbance at 340 nm (McComb et al., 1976); NADH is the donor for reactions run the other way, read as falling absorbance.

As a readout, the NAD+/NADH ratio needs its method stated. Enzymatic cycling assays split the sample: in a plate reader method validated on Arabidopsis leaf extracts, NAD+ and NADP+ were measured in HCl extracts and NADH and NADPH in parallel alkaline extracts (Queval and Noctor, 2007). LC-MS reads all four from one extract, but the forms interconvert during extraction; in cultured mammalian cells and mouse tissues, 40:40:20 acetonitrile:methanol:water with 0.1 M formic acid gave the least interconversion, followed by immediate neutralization (Lu et al., 2018).

Genetically encoded sensors read the free cytosolic ratio in living cells. Peredox joins a circularly permuted T-Sapphire GFP to the bacterial NADH-binding protein Rex and can be calibrated with exogenous lactate and pyruvate (Hung et al., 2011). SoNar is a bright, fast, pH-resistant sensor with a wide dynamic range, used in living cells, in vivo and in a screen of more than 5,500 compounds (Zhao et al., 2015). Extract totals and sensor ratios answer different questions, so state which one a figure shows.

Handling and Storage

The two forms degrade in opposite directions: NAD+ undergoes base-catalyzed degradation at high pH, NADH acid-catalyzed degradation at low pH (Wolfe et al., 2024). In a kinetics study of NADPH that included NADH, NADH degradation was close to first order in hydronium ion and in phosphate or acetate (Wu et al., 1986). Keep NAD+ stocks out of alkaline buffers and NADH out of acid, and neutralize acid extracts promptly (Lu et al., 2018).

At pH 8.5 over 43 days, Tris kept both forms most stable: NADH was lost at 4 µM per day at 19°C and 11 µM per day at 25°C, against up to 34 µM per day in sodium phosphate or HEPES, and the loss can be followed by UV-Vis because degradation runs through the dihydropyridine ring (Wolfe et al., 2024).

For the catalog NAD+, follow the storage instructions on the product page for the size you have, protect it from light and avoid freeze/thaw cycles once a solution is made; for the 200MG/ML liquid, also follow the bottle label. The vial buffer is not named, so check the pH after reconstitution. NADH reagent often comes as the disodium salt (709.4 g/mol, PubChem CID 44630232), so use the molar mass on its label. For molar work, use the content measured on the lot certificate, filed by lot number in the COA portal.

Questions Researchers Ask

What is the difference between NAD and NADH?

NAD+ is the oxidized form and NADH the reduced form of the same dinucleotide. NADH carries an extra hydride on the nicotinamide ring, absorbs at 340 nm and donates electrons; NAD+ accepts them and is the form PARPs, sirtuins and CD38 use up (Wilhelm and Hirrlinger, 2012).

Oxidized vs reduced NAD: how do labs tell them apart?

Only NADH absorbs at 340 nm (Wolfe et al., 2024), and the forms survive opposite extractions, so cycling methods measure NAD+ in acid extracts and NADH in alkaline ones (Queval and Noctor, 2007); LC-MS separates both from one extract if interconversion is controlled (Lu et al., 2018).

What does the NAD+/NADH ratio measure?

The redox state of a compartment: free ratios of about 725 in the cytoplasm of well-fed rat liver against about 8 in its mitochondria (Williamson et al., 1967). Peredox and SoNar report the free cytosolic ratio in living cells (Hung et al., 2011; Zhao et al., 2015).

Do sirtuins and PARPs use NADH?

Not in the studies that tested it. NADH inhibited Sir2 enzymes only at an average IC50 of 17 mM (Schmidt et al., 2004), and it was not a substrate for poly(ADP-ribose) synthetase or a microsomal NAD glycohydrolase in rat liver fractions (McCreanor and Bender, 1983).

Does Disguised Alpha sell NADH?

Not as a single compound. The catalog lists NAD+ as buffered lyophilized vials and a 200MG/ML liquid and its precursor NMN as 500MG capsules, for laboratory research use only. See the NAD+ research guide and the NMN vs NAD+ comparison.