NADH

NADH is the reduced form of nicotinamide adenine dinucleotide (NAD+), carrying high-energy electrons and a proton. It transfers reducing power in cellular metabolism.

NAD+/NADH redox couple: The interconvertible oxidized and reduced forms of nicotinamide adenine dinucleotide that transfer electrons in metabolism. NADH is the reduced member of this electron-transfer pair.
Nicotinamide adenine dinucleotide: A coenzyme composed of two nucleotides that serves as an electron carrier in cellular reactions. NADH is one redox form of this coenzyme.
Glycolysis: The cytosolic pathway that converts glucose into pyruvate while producing ATP and NADH. Glycolysis generates NADH when glyceraldehyde 3-phosphate is oxidized.
Mitochondrial redox shuttle: A transport-linked process that moves reducing equivalents between the cytosol and mitochondrial matrix. It determines how efficiently cytosolic NADH can support mitochondrial ATP production.
Electron transport chain: A series of membrane protein complexes that pass electrons to oxygen and use released energy to pump protons. NADH donates electrons to its first complex, helping drive proton pumping.
Nicotinamide: A pyridine-containing amide derived from vitamin B3 and found in the reactive end of NAD+ and NADP+. Its ring accepts the hydride that converts NAD+ into NADH.
Citric acid cycle: A cyclic pathway that oxidizes acetyl-CoA to carbon dioxide while producing reduced electron carriers and other products. Several of its reactions produce NADH for mitochondrial respiration.
Reactive oxygen species: Chemically reactive oxygen-containing molecules, including superoxide and hydrogen peroxide, produced in cells. Electron leakage during NADH-supported respiration can contribute to their formation.
Complex I: The respiratory-chain enzyme that oxidizes NADH, transfers its electrons to ubiquinone, and pumps protons across the inner mitochondrial membrane. This is the main entry point for mitochondrial NADH electrons into respiration.
Hydride ion: A hydrogen atom carrying two electrons and a negative charge, transferred in many biochemical oxidation-reduction reactions. NAD+ reduction adds a hydride to its nicotinamide ring.

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