NAD+ peptide: a coenzyme, not a peptide

Why NAD+ peptide is a misnomer worth explaining

NAD+ peptide is one of the most-searched terms in this category, and the molecule behind it is not a peptide. That is worth stating at the top, plainly, and without any suggestion that the person typing it has blundered. The term is doing an honest job. It means the NAD+ that research suppliers sell, in a vial, on the same page as the peptides. Searches for NAD+ peptide are looking for a coenzyme, and a coenzyme is what they find.

The catalogue is what attached the word. Suppliers group material by how it is handled rather than by chemical class, so NAD+ sits alongside BPC-157 and GHK-Cu because all three arrive as a white lyophilised powder in a sealed vial with a certificate written against the lot number. Anything on that shelf becomes a peptide in common usage. Search habits followed the shelving rather than the chemistry, and NAD+ peptide is the phrase that shelving produced.

The molecule has been on record for longer than most of what it is shelved beside. Arthur Harden and William John Young found it in 1906 as a heat-stable fraction of yeast extract that made fermentation run faster and that they could not name, so they called it a coferment. Warburg established what it actually does in 1936, showing that it carries a hydride from one reaction to another. Neither description has anything to do with amino acids, and the two vocabularies have only ever met on a shelf.

The distinction is still worth keeping, and not for the pleasure of correcting anyone. Peptides and coenzymes are different classes of molecule. They are characterised by different analytical methods, described on a certificate in different terms, and handled differently once a vial leaves the freezer. Anyone who arrives at NAD+ peptide expecting a sequence on the certificate will not find one, and the reason for that is structural.

Three practical things change for a NAD+ peptide buyer when the word changes. A buyer looking for a sequence on the certificate finds a formula and a CAS number instead. A buyer expecting the 10mg vial a peptide arrives in finds a gram of powder. And a buyer comparing purity figures across the two is comparing two analytical traditions that happen to share a percentage sign. None of that is a problem once the class is right, and all of it is confusing while the class is wrong.

What the molecule behind NAD+ peptide is made of

NAD+ stands for nicotinamide adenine dinucleotide, and the name is a description of the structure read from the outside in. It is a dinucleotide, meaning two nucleotides joined together. The join is a pyrophosphate bridge: a pair of phosphate groups set back to back between the two halves. On one side of that bridge is a ribose sugar carrying nicotinamide. On the other is a ribose sugar carrying adenine.

Read from either end, each half is a recognisable compound in its own right. The nicotinamide side is nicotinamide mononucleotide, the molecule sold separately as NMN. The adenine side is adenosine monophosphate, the AMP of basic biochemistry. NAD+ is those two joined through their phosphates, which is worth holding on to, because it explains most of the confusion further down this page: NMN is not a smaller grade of NAD+, it is one of its halves.

Every component in that description is a sugar, a phosphate group or a nitrogenous base. None of them is an amino acid, and there is no peptide bond anywhere in the molecule. A peptide bond is a specific linkage between the carboxyl group of one amino acid and the amino group of the next, formed by a condensation that releases a molecule of water. NAD+ contains neither of the partners that bond needs.

The plus sign belongs to the chemistry rather than to the product name. NAD exists in two interconvertible forms, and the oxidised form carries a positive charge on the nitrogen of the nicotinamide ring. Writing NAD+ rather than NAD states which of the two forms the material is. It is not a trademark flourish and not a grade marker, and it travels into the search term NAD+ peptide intact.

A coenzyme and a peptide are different kinds of thing

A peptide is defined by its bonds. Amino acids joined head to tail by peptide bonds form a chain, and that chain has a sequence: a defined order which can be written out one letter per residue and read from one end to the other. That is why a peptide listing quotes a string of capitals. Length, sequence and mass are the terms in which a peptide's identity is stated, and confirming that identity means confirming that the material in the vial matches the sequence claimed for it. That definition is set out in full in what is a peptide, and NAD+ satisfies no part of it: no amino acids, no peptide bonds, nothing to sequence.

A coenzyme is defined by its part in a reaction. It is a small organic molecule, not a protein, that an enzyme requires in order to carry out its chemistry, and its usual job is to carry something between reactions: an electron, a chemical group, a hydride. Coenzymes are not enzymes, and they are not built from amino acids. NAD+, the molecule behind the NAD+ peptide search, is the best known member of the class.

Cofactor is the wider word and it is worth separating from coenzyme, because the two are used interchangeably in product copy and mean different things in a textbook. A cofactor is anything an enzyme needs beyond its own protein, including metal ions such as the copper in GHK-Cu or the zinc in a metalloenzyme. A coenzyme is the organic subset of that, and a coenzyme that is passed between enzymes rather than locked into one of them, as NAD+ is, is sometimes called a cosubstrate. NAD+ answers to redox cofactor, coenzyme and cosubstrate depending on which reaction is being described, and to none of the words used for a chain of amino acids.

So NAD+ has no sequence, because there is nothing in it to sequence. It has a structure, which is drawn rather than spelled. It has no residues, so it cannot be described as long or short. It has no N-terminus and no C-terminus, so none of the questions that follow a peptide around apply to it in any form: acetylation, capping, truncation, which end a fragment was cut from.

That is why the word peptide in NAD+ peptide is not merely imprecise. It points at the wrong set of questions. Purity, identity and stability all mean something for NAD+, and all three are established by different means than they are for a chain of amino acids. A purity figure is the one term the two classes share, and even there the reading is worth doing carefully, because peptide purity, stated as a percentage, is a proportion of what the detector saw rather than a proportion of the vial.

Where NAD+ sits in metabolism, and the 340 nm readout

Naming the pathways is more useful than describing the chemistry in the abstract. NAD+ is the hydride acceptor in glycolysis, where glyceraldehyde-3-phosphate dehydrogenase reduces it to NADH. It is reduced again three times over in the citric acid cycle, and again in the fatty acid oxidation spiral. The NADH produced by all of that is what feeds electrons into the electron transport chain, which is the front half of oxidative phosphorylation. That is the whole of the classical account, and NAD+ appears in every step of it as the carrier rather than as a product.

The enzymes that do this have a family name worth knowing, because it is the reason the compound is a bench reagent at all. Dehydrogenases are enzymes that remove hydrogen from a substrate, and a large number of them use NAD+ as the acceptor: lactate dehydrogenase, alcohol dehydrogenase, aldehyde dehydrogenase, malate dehydrogenase, isocitrate dehydrogenase, glyceraldehyde-3-phosphate dehydrogenase. An assay for any one of those enzymes is, in practice, an assay for the coenzyme turning over.

Here is why that can be measured at all. NADH absorbs ultraviolet light strongly at 340 nm and NAD+ does not. The two forms are otherwise the same molecule, so a reaction that converts one into the other changes the absorbance of the solution at that wavelength and at almost no other. Put a cuvette in a spectrophotometer, or a plate on a reader, watch 340 nm, and the trace is a direct record of how fast the enzyme is working. The molar extinction coefficient of NADH at 340 nm is conventionally taken as 6,220 M⁻¹cm⁻¹, which is the constant that turns an absorbance change into a quantity of coenzyme.

It goes further than the NAD-dependent enzymes themselves. A reaction with no optical signal of its own can be linked to one that has: run the product of the first reaction into an NAD-linked dehydrogenase, and the absorbance change at 340 nm reports on both. Coupled assays built that way are how a great many enzyme activities and metabolite concentrations are measured, which is why a laboratory buying what it found under NAD+ peptide is often not studying the coenzyme at all. It is the instrument rather than the subject, and the quality of an instrument is worth knowing.

That single optical property is the practical answer to what a vial bought as NAD+ peptide is for on a bench, and it is the one that is almost never given. It is also the reason purity and identity matter more here than the percentage on the label suggests. When the reagent is the readout, anything in the vial that absorbs near 340 nm, or anything that is not the coenzyme at all, is measured as signal. A lot-matched certificate is not paperwork in that setting; it is the calibration of the experiment, which is why it is worth knowing how to read a peptide certificate of analysis line by line.

None of this is an account of what anything does in a person. It is a description of a coenzyme in the reactions it is studied in, all of them in cells, tissue preparations and model organisms. This material is supplied for in-vitro laboratory research only.

The NAD+/NADH couple, sirtuins and DNA repair

The chemistry NAD+ is studied for is a two-state one. NAD+ is the oxidised form. It accepts a hydride and becomes NADH, the reduced form. NADH can pass that hydride on and revert to NAD+. Written together as the NAD+/NADH couple, the pair is the central redox carrier of cellular metabolism, and the ratio between the two forms is itself a measurement: it is read as a report on the redox state of the preparation rather than as a quantity of anything.

Because the molecule cycles between the two forms rather than being spent, the same NAD+ can turn over again and again. That is classical coenzyme behaviour: carried, not consumed. Nothing built from amino acids behaves that way, which is the substance of the objection to NAD+ peptide as a name. What such work measures is the quantity present at a given moment and the ratio of one form to the other, not the disappearance of the molecule.

One more distinction belongs with the ratio, because it is where careless readings come from. A cell does not hold one pool of this coenzyme but several, kept apart by membranes: a nuclear and cytosolic pool on one side, a mitochondrial pool on the other, each with its own ratio of the two forms and its own supply. A measurement made on whole-cell lysate averages compartments that behave differently, so published work states which pool was sampled and by what method. A figure quoted without that qualification is missing the part that makes it comparable.

A second set of enzymes treats NAD+ differently. Sirtuins use it as a substrate rather than as a carrier, which means it is consumed in the reaction rather than handed back. There are seven mammalian sirtuins, SIRT1 to SIRT7, and every one of them requires the coenzyme to work at all. Sirtuin work is where NAD+ turns up in cellular ageing research models, and where the terms cellular senescence and oxidative stress enter the literature around it.

The PARP enzymes consume it the same way. PARP is short for poly(ADP-ribose) polymerase, a family that detects breaks in DNA and tags the site by building chains of ADP-ribose, a unit it takes from NAD+ one molecule at a time. DNA repair is therefore a draw on the same pool the sirtuins are drawing from, and PARP1 is generally described as the largest single consumer in a cell. A third enzyme, the ectoenzyme CD38, consumes it again on its own account, and it is named often in the ageing literature for that reason.

That competition between several families for one shared pool is the shape of a great deal of the published work. It is a constraint that model systems are designed around rather than an outcome anyone has measured in a person. All of this literature is preclinical and all of it sits in model systems. This material is supplied for in-vitro laboratory research only.

Where a cell gets its NAD+: three biosynthesis routes

A cell makes NAD+ by three named routes, and the names are worth having because the precursor compounds sold alongside it are named after the steps in them. Nothing in this section describes a supplement or an intake. It is the biochemistry of how the molecule is assembled, which is the context the preclinical literature is written in. No ribosome and no amino acid appears anywhere in it, which is the structural reason NAD+ peptide is the wrong name for the product of these routes.

The de novo route builds it from tryptophan through the kynurenine pathway, a long sequence of steps that arrives eventually at quinolinic acid and from there at the nicotinamide ring. The Preiss-Handler route is shorter and starts from nicotinic acid, one of the two compounds that the name vitamin B3 covers. The salvage route is the busiest of the three: it recovers the nicotinamide released whenever a sirtuin or a PARP enzyme breaks the molecule apart, and recycles it rather than building a new ring from scratch.

Two enzymes carry most of the traffic in that last route. NAMPT, nicotinamide phosphoribosyltransferase, attaches nicotinamide to a ribose phosphate to make NMN, and it is the rate-limiting step. NMNAT, nicotinamide mononucleotide adenylyltransferase, then joins NMN to an AMP unit, which is the reaction that forms the pyrophosphate bridge and finishes the molecule. NMNAT1 does that work in the nucleus, and NMNAT2 and NMNAT3 elsewhere in the cell.

That last step is the clearest way to see what NMN and nicotinamide riboside actually are. They are not weaker versions of NAD+ and they are not a different grade of it. They are the intermediates one and two steps back along the salvage route, which is why they are sold under their own names, with their own formulas and their own CAS numbers, and why they belong in the disambiguation table below rather than in a comparison of strengths. A search for NAD+ peptide returns all three names together, which is what makes the distinction worth drawing.

What NAD+ peptide is confused with, and what it is not

Several molecules sit close enough to NAD+ to be mistaken for it, and the NAD+ peptide search term collects all of them. None of them is a peptide either, so the correction in this article travels to every one.

NADH is the same molecule in its reduced state, not a separate compound. NADP+ is NAD+ carrying an additional phosphate group on the adenine-side ribose, which makes it a different coenzyme with its own formula and its own CAS number, used by a different set of enzymes in reductive biosynthesis rather than in energy metabolism. Nicotinamide mononucleotide and nicotinamide riboside are smaller: a single nucleotide in the first case, and a ribose carrying nicotinamide with no phosphate at all in the second. All four are nucleotide chemistry. None of them has an amino acid in it.

The peptides NAD+ is shelved beside are a genuinely different class. MOTS-c is a mitochondrially encoded peptide of sixteen residues; GHK-Cu is a copper-binding tripeptide of three. Both are chains of amino acids with a sequence that can be written out, and both are documented that way, as the MOTS-c peptide profile and the GHK-Cu copper peptide profile set out. NAD+ shares their vial, their powder and their certificate format, and nothing else.

A third kind of confusion arrives from outside the laboratory category entirely. NAD+ peptide serum and NAD+ peptide cream are cosmetic products, formulated and regulated as cosmetics, and they are sold by the bottle with an ingredients list rather than by the lot with a certificate. They are named for the same molecule and they are not the same category of thing as a sealed vial of assayed powder. Nothing on this page describes them.

The last confusion is the smallest and the most common. NAD and NAD+ are not two products. They are one molecule written two ways, and the plus sign simply states that the oxidised form is meant. A listing for a 1000mg NAD+ vial and a listing for NAD 1000mg would be the same material, and both are what a search for NAD+ peptide is looking for.

How the material sold as NAD+ peptide is supplied, stored and handled

NAD+ is supplied as a white to off-white lyophilised powder in a 1000mg vial. That is the first thing that surprises anyone arriving at NAD+ peptide from the peptide catalogue, where vials run from 5mg to 100mg. The vial holds far more material than a peptide vial does, and the category it sits in here is Longevity Research rather than any of the peptide groupings. Lyophilised is the British spelling; most American listings write lyophilized, and it is the same freeze-drying step either way.

Storage is −20°C for the long term, protected from light and moisture. That protection clause is not boilerplate carried across from a peptide label. NAD+ is light-sensitive and hygroscopic, and it is readily soluble in water, which together mean that the air a vial is opened into is a real variable rather than a theoretical one. Hygroscopic has a visible consequence: a dry cake exposed to room air takes up water from it, and a cake that has slumped, gone glassy at the edges or darkened has been telling you something about how it was kept. Keeping it dark, keeping it sealed and keeping its time at room temperature short is the whole of the handling story, and it is the same discipline set out in the guide to how to store peptides at −20°C.

In water it behaves like most lyophilised material and rather worse than some. An aqueous solution of NAD+ is measurably less stable than the dry solid, which is the reason the compound ships dry and is lyophilised in the first place. Once it is in water it is held cold, at 2°C to 8°C, and dark for whatever in-use period the work allows. Bacteriostatic water is the diluent held alongside the catalogue for lyophilised research material, and what it is and how it differs from plain sterile water is set out in the note on bacteriostatic water for peptides. Repeated freeze-thaw cycles are the other thing worth avoiding once material is in solution, for the ordinary reason that each cycle is another chance for the compound to come apart.

Purity is quoted by HPLC, as it is for the peptides, and the released figure is 99.94%. Identity is where the two part company. A peptide certificate reports a sequence and the mass that sequence predicts, and the analysis confirms the two agree. NAD+ has no sequence to confirm, so its documentation speaks in the compound's own terms rather than in a string of residues: formula, molecular weight, CAS number, and an LC-MS identity confirmation.

Why a vial is labelled NAD 500 or NAD 1000

NAD 500 and NAD 1000 are searched almost as often as NAD+ peptide itself, and the number in each is the fill mass in milligrams. It is not a concentration, not a strength and not a grade. A vial marked NAD 1000 holds a nominal one gram of the same powder a vial marked NAD 500 holds half a gram of, assayed by the same method against the same specification.

The listing here is a single 1000mg vial at $99.99. The certificate archive is wider than the listing, because it records what the laboratory tested rather than what is currently in stock: lots of 100mg, 500mg and 1000mg are all on file, and they stay on file after a lot has sold through. That is the reason the table below carries fills the shop does not sell.

Reading several lots side by side is the reason for publishing them all. A single figure on a website is a claim. Eight lots, each named, each dated, each assayed by an independent laboratory, are a record that can be checked against the vial in hand. The number printed on the label goes into the lot number checker and the certificate for that exact batch comes back. A nominal fill mass is the one thing a NAD+ peptide listing and a peptide listing state in the same terms.

What a certificate states when there is no sequence

A certificate for a peptide and a certificate for a coenzyme carry the same fields and fill two of them differently. Anyone who reached this page through NAD+ peptide is reading the coenzyme column. Both name the lot, the laboratory, the date, the appearance, the purity method and the figure it returned. The difference is in the identity line, and it follows directly from the chemistry: a peptide's identity is its sequence and the mass that sequence predicts, and NAD+ has no sequence, so identity is stated as the formula, the molecular weight, the CAS number and an LC-MS confirmation against a reference standard.

It is worth being specific about what the LC-MS line establishes for a molecule of this shape. Mass spectrometry weighs what comes off the column, so a confirmation at the expected mass says the intact dinucleotide is what is present, bridge included. The failure modes it would catch are the obvious ones: a molecule that has come apart at the pyrophosphate bridge appears as its two halves, nicotinamide mononucleotide at 334.22 g/mol and adenosine monophosphate, at masses nowhere near 663.43. The chromatography and the mass measurement answer different questions, which is why a certificate carries both and neither one on its own.

Grade is the other thing people try to read off a certificate, and it is worth being exact about. Research grade, pharmaceutical grade and food grade are descriptions of the specification a material was made and tested against, not properties a vial has in itself. A grade word on a label is a claim; the certificate is the evidence for it, and the only certificate that evidences anything about a particular vial is the one written against the lot number printed on that vial. Everything sold here is laboratory research material, documented lot by lot, and the archive is published in full rather than by exception.

That is also why a lot that is no longer for sale stays in the library. A certificate archive with only current stock in it is a marketing page. One that keeps every lot, including the one that measured 99.40% and the one that came in at 957.53mg against a nominal gram, is a record. The same reasoning is set out at greater length in the note on how to vet a research peptide supplier. That archive, rather than the word peptide in NAD+ peptide, is what any claim about a particular vial rests on.