Is NAD+ a peptide, or a coenzyme?

No: NAD+ is not a peptide. Nicotinamide adenine dinucleotide is a dinucleotide coenzyme, two nucleotides joined through their phosphates, and there is not a single amino acid or peptide bond anywhere in it. The question keeps coming up because NAD+ is sold by research-peptide suppliers (we list it as the NAD+ Kit) and "NAD peptide" has become a common search phrase. This guide treats NAD+ the way a chemist would: what the molecule is, what its plus sign means, how it carries electrons, which enzymes use it up, how cells make it, how it compares with the precursors NMN and NR, and what governs its stability on the bench.

Research use only. NAD+ is sold here for in-vitro laboratory research. It is not for human or veterinary use and has not been evaluated by the FDA. This page covers chemistry and cell biochemistry only.

NAD+ at a glance

Why "NAD peptide" is the wrong label

The words get attached by association: NAD+ comes from the same vendors, sits in the same freezers and comes up in the same online threads as research peptides. Chemically the two classes have almost nothing in common.

The label matters because it sets expectations about analysis. There is no sequence to read by tandem mass spectrometry and no amino acid composition to check. Identity for NAD+ rests on its mass, its UV spectrum and its chromatographic behavior, which are covered further down.

What the "+" in NAD+ means

The plus sign marks the positive charge on the ring nitrogen of nicotinamide in the oxidized form, which makes that ring a pyridinium ion. It is not the charge on the whole molecule. The pyrophosphate bridge carries two negative charges at neutral pH, so NAD+ as a whole sits at a net charge of about minus one. When the ring takes up a hydride it loses that positive charge, which is why the reduced form is written NADH with no plus sign. Many papers write "NAD" when the redox state does not matter, and "NAD(H)" or "NAD(P)H" when they mean both forms or both coenzymes.

From cozymase to NAD+: names in older literature

The molecule was found long before its structure was known. In 1906 Arthur Harden and William Young reported that fermentation in yeast juice depended on a small, heat-stable factor that passed through a dialysis membrane, and they called it cozymase. Hans von Euler-Chelpin went on to characterize it as a nucleotide, and he and Harden shared the 1929 Nobel Prize in Chemistry for their work on sugar fermentation. In the mid-1930s Otto Warburg's laboratory showed that the pyridine portion, the nicotinamide ring, is the part that carries hydrogen. Conrad Elvehjem's work in the same decade identified nicotinic acid and nicotinamide as the vitamin precursors of the coenzyme.

For decades the literature called NAD+ diphosphopyridine nucleotide (DPN) and NADP+ triphosphopyridine nucleotide (TPN). The current names replaced them during the 1960s, so a thorough search of older work needs both sets of terms.

Redox chemistry: a hydride on carbon 4

In its redox role NAD+ accepts two electrons and one proton, chemically a hydride ion, at carbon 4 of the nicotinamide ring. The product is NADH, and a second proton is released to solution:

NAD+ + 2e⁻ + H⁺ ⇌ NADH

Dehydrogenases catalyze this transfer, and each one delivers the hydride to one particular face of the flat ring, so the reaction is stereospecific. The standard reduction potential of the NAD+/NADH couple at pH 7 is about −0.32 V. The coenzyme is recycled rather than used up: it moves back and forth between the two forms as glycolysis, the TCA cycle and mitochondrial respiration oxidize their substrates, and the NAD+/NADH ratio is one of the most widely measured indicators of a cell's redox state.

Reduction also changes the spectrum, which is the single most useful practical fact about the molecule. Both forms absorb at 260 nm through the adenine ring. Only NADH absorbs at 340 nm, with a molar absorptivity of about 6,220 M⁻¹ cm⁻¹, and only NADH fluoresces, emitting around 460 nm when excited at 340 nm. Classic enzyme assays follow dehydrogenase reactions by watching that 340 nm band rise or fall, and a preparation sold as NAD+ that shows meaningful absorbance at 340 nm contains reduced material.

NADP+ uses the same ring and the same chemistry, and its standard potential is nearly identical. The extra 2′-phosphate, added to NAD+ by the enzyme NAD kinase, is a recognition tag that lets enzymes tell the two coenzymes apart. Cells exploit that difference by keeping the NAD pool largely oxidized and the NADP pool largely reduced, so NAD+ mostly accepts electrons from catabolic pathways while NADPH mostly donates them to biosynthesis and to the glutathione system.

Recycled or consumed: the second job of NAD+

The redox role leaves NAD+ intact. A second group of enzymes destroys it. They break the bond between nicotinamide and its ribose, release free nicotinamide, and put the ADP-ribose part to use:

Each turnover of these enzymes spends one NAD+ molecule that the cell then has to rebuild. That is why the NAD+ level in a culture is better treated as the balance between synthesis and consumption than as a fixed quantity, and why an assay of a consuming enzyme depends on how much intact NAD+ was present at the start. Nicotinamide, the shared by-product, is itself an inhibitor of sirtuins, a detail worth controlling for in deacylation assays.

Routes into the NAD+ pool

Cells can build NAD+ from several starting points, and the routes meet at a common step:

Two papers from 2004 anchor the salvage side. Working in mouse fibroblasts, Revollo and colleagues found NAMPT to be the rate-limiting component of the nicotinamide route: raising NAMPT, but not NMNAT, increased total cellular NAD. In the same year Bieganowski and Brenner showed that nicotinamide riboside is an NAD+ precursor through dedicated nicotinamide riboside kinases conserved from yeast to humans, a route that does not pass through nicotinic acid mononucleotide. Humans have three NMNAT enzymes, NMNAT1 to NMNAT3, located mainly in the nucleus, the Golgi and cytosol, and mitochondria respectively.

NAD+, NMN and NR as chemicals

The three names travel together, but they are different compounds at different points in the same network:

For in-vitro work the differences are physical as much as biological. The three differ in size, in charge and in how they cross membranes, so a cell's response to one depends on transport and on its conversion machinery, not just on the end product. Their spectra differ too: NR and NMN lack the adenine ring, so their absorbance near 260 nm comes from nicotinamide alone and is much weaker than that of NAD+, and a concentration calibrated for one cannot be read across to the others. A result obtained with NR or NMN describes that compound and the cell's capacity to convert it; it is not a result about NAD+ added directly.

Compartments: one molecule, several pools

A cell's NAD+ is not one well-mixed pool. The nucleus and cytosol exchange freely through nuclear pores, while mitochondria hold a separate pool behind an inner membrane that NADH cannot cross. Reducing equivalents made in the cytosol reach the mitochondria indirectly, through the malate-aspartate and glycerol-3-phosphate shuttles.

Whether mammalian mitochondria can import intact NAD+ was argued for years. In 2020 the carrier SLC25A51 was identified as a mammalian mitochondrial NAD+ transporter; cells lacking it had less mitochondrial NAD+ while whole-cell NAD+ was unchanged. The practical point for experimental design is that a whole-cell NAD+/NADH figure averages compartments that can sit at very different ratios, which is why genetically encoded sensors targeted to individual compartments have become common in the field.

Stability as chemistry

NAD+ is less robust than its central role might suggest, and its reduced form is fragile under the opposite conditions:

• pH. The oxidized form is most vulnerable in alkaline solution, where hydroxide attacks the positively charged nicotinamide ring and the nicotinamide-ribose bond breaks, releasing nicotinamide and ADP-ribose. NADH is the mirror image: acid catalyzes the addition of water across its reduced ring, and breakdown speeds up as pH falls. Kinetic work on NADPH and NADH found the degradation rate tracks hydronium ion concentration and temperature.
• Buffer identity. The buffer species matters as well as the pH. The same kinetic study found that phosphate and acetate accelerate loss of the reduced cofactors, and a 2024 comparison running for 43 days found both NAD+ and NADH highly stable in Tris, with faster NADH loss in sodium phosphate and HEPES.
• Temperature. Rates climb with temperature. In the 2024 study, even the step from 19 °C to 25 °C made a significant difference to long-term NADH stability.
• Light. NADH absorbs in the near-ultraviolet, and protecting the reduced form from strong light is routine bench practice.
• Hydrolysis by other routes. The pyrophosphate bridge can also be cleaved, chemically or by nucleotide pyrophosphatases present in biological extracts, giving NMN and AMP.

None of this is visible. A degraded NAD+ solution looks the same as a fresh one, so the checks are spectroscopic and chromatographic: absorbance at 340 nm for reduced contamination, and reversed-phase HPLC for nicotinamide and ADP-ribose peaks that elute separately from the parent.

What a certificate for NAD+ should show

• Chromatographic purity by reversed-phase HPLC with UV detection at 260 nm, ideally with the chromatogram rather than a bare percentage.
• Identity that fits a dinucleotide: a mass consistent with the stated salt form, and a UV spectrum peaking near 260 nm with little or nothing at 340 nm.
• The salt form named, free acid or sodium salt, since it changes the formula weight and so the meaning of any stated mass.
• A batch number that matches the container, with the analysis date.

Our batch certificates are published in the COA library, and the Certificate of Analysis guide explains how to read one.

NAD+ supply in the United States

The NAD+ Kit is dispatched cold-chain from the warehouse that serves the United States, with tracked delivery across the country next business day. It is priced in US dollars and payable by Visa, Mastercard or Apple Pay, and its batch certificate is in the COA library. This guide does not describe the kit's packaging or contents; if those details matter to your protocol, contact support before ordering, and follow the storage statement on the container.

Regulatory position

The NAD+ we supply is not an FDA-approved drug, has not been evaluated by the FDA and is not sold as a dietary supplement. It is a research material for in-vitro laboratory work only and is not for human or veterinary use.

What this page leaves out

This guide gives no amounts, schedules or preparation-for-use instructions and does not discuss any use of NAD+ in people or animals. We supply research materials; we are not a clinic.

Related reading

• What are research peptides? · How to read a Certificate of Analysis · Bac water and solution stability · What is MOTS-c?