Diaphorase enzymes are a class of dehydrogenase enzymes that catalyze reactions involving the nicotinamide adenine dinucleotide cofactors. Two specific members of this enzyme class, denoted as NADH diaphorase and NADPH diaphorase, are responsible for dehydrogenating the reduced forms of NAD and NADP, respectively. These enzymes, which occur naturally in all animal tissues, were first extracted in pure form by Straub in 1939.


Mechanism of Action

Within the nicotinamide adenine dinucleotide family of compounds, two members (NAD and NADP) act as hydride acceptors, while their respective reduced forms (NADH and NADPH) act as hydride donors. The role of the diaphorase enzymes is to transfer hydrogen ions between donor and acceptor molecules. The dehydrogenation of the reduced form NADPH, for example, requires the target molecule itself, an H+ ion and an acceptor molecule. The result of this reaction is therefore one NADP molecule and a reduced acceptor.

AG Scientific's Diaphorase Enzymes

SKU Product CAS
N-1181 Diaphorase (NADH) 9032-20-6
N-1185 Diaphorase (NADPH) 9001-68-7

Role of Diaphorase Enzymes in Living Tissues

Through the mechanism of transferring electrons between reduced and oxidized forms of NAD, the diaphorase enzymes support a number of critical processes in living tissues. One such process is the ongoing conversion of methemoglobin into ordinary hemoglobin. In this process, NADH diaphorase works in conjunction with cytochrome b5 reductase to oxidize NADH and reduce methemoglobin, thus producing hemoglobin. Deficiencies of NADH diaphorase and cytochrome b5 reductase in leukocytes and platelet cells are therefore associated with hereditary methemoglobinemia.


Blood platelets


NADPH diaphorase is also known to play a role in specific types of neurons. Non-pyramidal neurons with high concentrations of NADPH diaphorase synthesize nitric oxide, a compound that is essential to various aspects of brain and nervous system function. Specifically, nitric oxide is known to cause the release of certain neurotransmitters and neuroactive amino acids. NO has also been shown to support the expression of proteins linked to neuroplasticity.

Neurons structure

Current Areas of Research

Owing to their close association with the cofactor NAD, diaphorase enzymes have played an important role in recent research into this compound's role in the aging process. Recent research has shown that NAD levels decrease with age, resulting in reduced expression of sirtuin proteins and mitochondrial function, among other downstream effects. In several studies relating to the role of NAD in mitochondrial aging, diaphorase enzymes have been used as a component of cycling assay mixtures.

Elderly citizens

Other research has dealt with the role of NADPH dehydrogenase quinone 1, otherwise known as DT-diaphorase or DTD, in certain types of cancer. In several varieties of tumorous cells, DTD levels increase beyond their normal levels in non-tumorous tissues. As a result, DTD has been studied as a potential target for new classes of chemotherapeutic agents. Though potentially effective, research into DTD as a chemotherapeutic target requires the development of drugs other than the widely used Mitomycin C, which requires specific pH conditions in order to be metabolized.

Vial of Mitomycin C from AG Scientific, Inc. with water splash

AG Scientific's Mitomycin C, Stem Cell Reagent


  • Adler, Erich, H. V. Euler, and G. Günther. "Diaphorase I and II." Nature 143.3624 (1939): 641.
  • Stein, Abraham M., and Jeanne H. Stein. "Studies on the Straub diaphorase. I. Isolation of multiple forms." Biochemistry4.8 (1965): 1491-1500.
  • “Nicotinamide Adenine Dinucleotide.” Nicotinamide Adenine Dinucleotide - an Overview | ScienceDirect Topics, Science Direct, 2019, www.sciencedirect.com/topics/neuroscience/nicotinamide-adenine-dinucleotide.
  • “NADPH Dehydrogenase Activity.” NADPH Dehydrogenase Activity Gene Ontology Term (GO:0003959), 2019, www.informatics.jax.org/vocab/gene_ontology/GO:0003959.
  • “Methemoglobin.” Methemoglobin - an Overview | ScienceDirect Topics, Science Direct, 2019, www.sciencedirect.com/topics/medicine-and-dentistry/methemoglobin.
  • Takeshita, M., et al. "Alteration of NADH-diaphorase and cytochrome b5 reductase activities of erythrocytes, platelets, and leucocytes in hereditary methaemoglobinaemia with and without mental retardation." Journal of medical genetics 19.3 (1982): 204-209.
  • Hope, Bruce Thomas, et al. "Neuronal NADPH diaphorase is a nitric oxide synthase." Proceedings of the National Academy of Sciences 88.7 (1991): 2811-2814.
  • Kuriyama, Kinya, and Seitaro Ohkuma. "Role of nitric oxide in central synaptic transmission: effects on neurotransmitter release." The Japanese Journal of Pharmacology 69.1 (1995): 1-8.
  • Gallo, Eduardo F., and Costantino Iadecola. "Neuronal nitric oxide contributes to neuroplasticity-associated protein expression through cGMP, protein kinase G, and extracellular signal-regulated kinase." Journal of Neuroscience 31.19 (2011): 6947-6955.
  • Johnson, Sean, and Shin–ichiro Imai. "NAD+ biosynthesis, aging, and disease." F1000Research 7 (2018).
  • Li, Wei, and Anthony A. Sauve. "NAD+ Content and its role in mitochondria." Mitochondrial Regulation. Humana Press, New York, NY, 2015. 39-48.
  • Davila, Antonio, et al. "Nicotinamide adenine dinucleotide is transported into mammalian mitochondria." Elife 7 (2018): e33246.
  • Frederick, David W., et al. "Increasing NAD synthesis in muscle via nicotinamide phosphoribosyltransferase is not sufficient to promote oxidative metabolism." Journal of Biological Chemistry 290.3 (2015): 1546-1558.
  • Danson, Sarah, et al. "DT-diaphorase: a target for new anticancer drugs." Cancer treatment reviews 30.5 (2004): 437-449.



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