Target type: molecularfunction
Catalysis of the reaction: NADH + H+ + a quinone = NAD+ + a quinol. [EC:1.6.5.9, GOC:mah, RHEA:46160]
NADH:ubiquinone reductase (non-electrogenic) activity is a key enzymatic step in the electron transport chain, a fundamental process in cellular respiration. This activity catalyzes the transfer of electrons from NADH, a reduced form of nicotinamide adenine dinucleotide, to ubiquinone (also known as coenzyme Q), a lipid-soluble electron carrier. This transfer occurs within the mitochondrial inner membrane, a highly specialized membrane in eukaryotic cells.
The non-electrogenic nature of this reaction implies that the transfer of electrons does not directly generate a proton gradient across the membrane, which is a crucial aspect of ATP synthesis. However, this reaction indirectly contributes to the proton gradient by facilitating the transfer of protons from the mitochondrial matrix to the intermembrane space through a series of proton-pumping complexes that are also part of the electron transport chain.
Specifically, NADH:ubiquinone reductase (non-electrogenic) activity functions in the following manner:
1. **NADH Binding:** NADH, carrying two electrons, binds to the enzyme's active site.
2. **Electron Transfer:** The enzyme facilitates the transfer of two electrons from NADH to a flavin mononucleotide (FMN) cofactor within the enzyme.
3. **Ubiquinone Reduction:** The electrons are then transferred to ubiquinone, reducing it to ubiquinol (QH2).
4. **Proton Translocation:** While this reaction itself is non-electrogenic, the reduced ubiquinol subsequently interacts with other electron transport chain complexes, such as cytochrome bc1 complex, which actively pump protons across the membrane, contributing to the electrochemical gradient.
This electrochemical gradient is ultimately harnessed by ATP synthase to generate ATP, the primary energy currency of cells. Therefore, the non-electrogenic NADH:ubiquinone reductase activity is a critical component of the complex machinery that drives cellular energy production.'
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| Protein | Definition | Taxonomy |
|---|---|---|
| NAD | An NAD(P)H dehydrogenase [quinone] 1 that is encoded in the genome of human. [PRO:DNx, UniProtKB:P15559] | Homo sapiens (human) |
| Compound | Definition | Classes | Roles |
|---|---|---|---|
| 4'-bromoflavone | 4'-bromoflavone: structure in first source | ||
| beta-naphthoflavone | beta-naphthoflavone : An extended flavonoid resulting from the formal fusion of a benzene ring with the f side of flavone. beta-Naphthoflavone: A polyaromatic hydrocarbon inducer of P4501A1 and P4501A2 cytochromes. (Proc Soc Exp Biol Med 1994 Dec:207(3):302-308) | extended flavonoid; naphtho-gamma-pyrone; organic heterotricyclic compound | aryl hydrocarbon receptor agonist |
| beta-lapachone | beta-lapachone : A benzochromenone that is 3,4-dihydro-2H-benzo[h]chromene-5,6-dione substituted by geminal methyl groups at position 2. Isolated from Tabebuia avellanedae, it exhibits antineoplastic and anti-inflammatory activities. beta-lapachone: antineoplastic inhibitor of reverse transcriptase, DNA topoisomerase, and DNA polymerase | benzochromenone; orthoquinones | anti-inflammatory agent; antineoplastic agent; plant metabolite |
| vitamin k 3 | Vitamin K 3: A synthetic naphthoquinone without the isoprenoid side chain and biological activity, but can be converted to active vitamin K2, menaquinone, after alkylation in vivo. | 1,4-naphthoquinones; vitamin K | angiogenesis inhibitor; antineoplastic agent; EC 3.4.22.69 (SARS coronavirus main proteinase) inhibitor; human urinary metabolite; nutraceutical |
| sulforaphane | sulforaphane : An isothiocyanate having a 4-(methylsulfinyl)butyl group attached to the nitrogen. sulforaphane: from Cardaria draba L. | isothiocyanate; sulfoxide | antineoplastic agent; antioxidant; EC 3.5.1.98 (histone deacetylase) inhibitor; plant metabolite |
| c 1303 | C 1303: DNa-binding drug; structure given indicates that the cpd should be the dimethylamino cpd, but it is named as the diethylamino cpd | ||
| nsc 366140 | NSC 366140: a 9-methoxypyrazoloacridine; structure given in first source | ||
| 5-methoxy-1,2-dimethyl-3-((4-nitrophenoxy)methyl)indole-4,7-dione | 5-methoxy-1,2-dimethyl-3-((4-nitrophenoxy)methyl)indole-4,7-dione: structure in first source | ||
| bisantrene | |||
| 4,3',5'-tri-o-methylpiceatannol | |||
| memoquin | memoquin: structure in first source | ||
| dicumarol | Dicumarol: An oral anticoagulant that interferes with the metabolism of vitamin K. It is also used in biochemical experiments as an inhibitor of reductases. | hydroxycoumarin | anticoagulant; EC 1.6.5.2 [NAD(P)H dehydrogenase (quinone)] inhibitor; Hsp90 inhibitor; vitamin K antagonist |
| ethyl biscoumacetate | Ethyl Biscoumacetate: A coumarin that is used as an anticoagulant. It has actions similar to those of WARFARIN. (From Martindale, The Extra Pharmacopoeia, 30th ed, p226) | hydroxycoumarin | |
| nsc 158393 | NSC 158393: structure given in first source |