NAD⁺: the pathway in the body

This page shows the biochemical pathway behind the laboratory value NAD⁺ (nicotinamide adenine dinucleotide): which stations follow one another, which enzymes carry out each step and which cofactors they use. Every statement has a source. The page describes general textbook knowledge and says nothing about any individual person.

In brief

NAD⁺ (nicotinamide adenine dinucleotide) is a coenzyme that the body forms from tryptophan or from forms of vitamin B3. It transfers hydrogen in many metabolic reactions and serves enzymes such as sirtuins and PARP as a substrate.

The pathway step by step

1. Tryptophan → Quinolinic acid Kynurenine pathway · Haem iron, Vitamin B6 (PLP) Quinolinic acid forms over several steps of the kynurenine pathway. The first step opens the ring of tryptophan; the enzyme for this carries haem iron, and a later step needs vitamin B6. Source 3
2. Quinolinic acid → NaMN QPRT · PRPP The enzyme QPRT attaches quinolinic acid to the sugar unit PRPP, releasing carbon dioxide. This forms nicotinic acid mononucleotide (NaMN). Source 2
3. NaMN → NaAD NMNAT1-3 · ATP Enzymes of the NMNAT family attach an adenine unit from ATP to NaMN. They work in the nucleus, the cytoplasm and the mitochondrion. Source 2
4. NaAD → NAD⁺ NAD synthetase · Glutamine, ATP NAD synthetase swaps the acid group for an amide group from glutamine. NAD⁺ is then complete. Source 2
5. NMN → NAD⁺ NMNAT1-3 · ATP NAD synthetase swaps the acid group for an amide group from glutamine. NAD⁺ is then complete. Source 2
6. NAD⁺ in metabolism → NADH Dehydrogenases In glycolysis, fatty acid breakdown and the citric acid cycle, dehydrogenases remove hydrogen from nutrients and transfer it to NAD⁺. This produces NADH. Source 1
7. NADH → Respiratory chain Complex I NADH passes its electrons to complex I of the respiratory chain. This produces ATP, and NAD⁺ becomes available again. Source 1
8. NAD⁺ in metabolism → Nicotinamide Sirtuins, PARP, CD38 Sirtuins, PARP and CD38 actually split NAD⁺: sirtuins remove acetyl groups from proteins, PARP works at DNA breaks, CD38 breaks NAD⁺ down. Each time, nicotinamide is left over. Source 1, 2
9. NAD⁺ in metabolism → NADP⁺ NAD kinase · ATP NAD kinase attaches a phosphate group to NAD⁺. NADP⁺ and its loaded form NADPH are kept separately and serve to build fats and to handle reactive oxygen species. Source 4

Cofactors in this pathway

• Niacin (vitamin B3) — Nicotinic acid and nicotinamide are precursors from which the cell builds NAD⁺ Source 1, 2
• Tryptophan — Starting material of the kynurenine pathway, which ends in quinolinic acid for NAD⁺ Source 3In the ORY catalogue as a laboratory value: Tryptophan
• Vitamin B6 — As pyridoxal phosphate, cofactor of a step in the kynurenine pathway Source 3In the ORY catalogue as a laboratory value: Vitamin B6
• Iron — As haem iron, cofactor of the enzyme that opens the tryptophan ring Source 3In the ORY catalogue as a laboratory value: Eisen
• Glutamine — Provides NAD synthetase with the amide group Source 2In the ORY catalogue as a laboratory value: Glutamin
• Magnesium — Forms the complex with ATP that NMNAT and NAD kinase act on Source 5, 2In the ORY catalogue as a laboratory value: Magnesium

Sources

1. Covarrubias AJ, Perrone R et al. NAD(+) metabolism and its roles in cellular processes during ageing. Nat Rev Mol Cell Biol 2021 · PubMed 33353981
2. Chini CCS, Zeidler JD et al. Evolving concepts in NAD(+) metabolism. Cell Metab 2021 · PubMed 33930322
3. Badawy AA. Kynurenine Pathway of Tryptophan Metabolism: Regulatory and Functional Aspects. Int J Tryptophan Res 2017 · PubMed 28469468
4. Oka SI, Titus AS et al. Molecular properties and regulation of NAD(+) kinase (NADK). Redox Biol 2023 · PubMed 36512915
5. de Baaij JH, Hoenderop JG, Bindels RJ. Magnesium in man: implications for health and disease. Physiol Rev 2015 · PubMed 25540137

Related pathways

• Kynurenine pathway — tryptophan
• Lactate and pyruvate — respiratory chain
• Serotonin and melatonin — tryptophan
• Dopamine, noradrenaline, adrenaline — Vitamin B6, Eisen
• Alanine — Vitamin B6, Magnesium

As of 2026-09-16. Draft written by Claude to schema v2; sources checked in PubMed; expert review pending
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