An electron transport chain(ETC) couples a chemical reaction between an electron donor (such as NADH) and an electron acceptor (such as O₂) to the transfer of H⁺ ions across a membrane, through a set of mediating biochemical reactions. These H⁺ ions are used to produce adenosine triphosphate (ATP), the main energy intermediate in living organisms, as they move back across the membrane. In mitochondria, it is the conversion of oxygen to water, NADH to NAD+ and succinate to fumarate that drives the transfer of H⁺ ions. Source: [Wikipedia](https://en.wikipedia.org/wiki/Electron_transport_chain) Proteins on this pathway have targeted assays available via the [CPTAC Assay Portal](https://assays.cancer.gov/available_assays?wp_id=WP111) dc1 e55 ac6 22902835 PubMed NDUFA4 is a subunit of complex IV of the mammalian electron transport chain. Cell Metab 2012 Balsa E Marco R Perales-Clemente E Szklarczyk R Calvo E Landázuri MO Enríquez JA electron transport chain pathway PW:0000034 Pathway Ontology 23746447 PubMed NDUFA4 mutations underlie dysfunction of a cytochrome c oxidase subunit linked to human neurological disease. Cell Rep 2013 Pitceathly RD Rahman S Wedatilake Y Polke JM Cirak S Foley AR Sailer A Hurles ME Stalker J Hargreaves I Woodward CE Sweeney MG Muntoni F Houlden H Taanman JW Hanna MG classic metabolic pathway PW:0000002 Pathway Ontology 30030361 PubMed Assembly of mammalian oxidative phosphorylation complexes I-V and supercomplexes. Essays Biochem 2018 Signes A Fernandez-Vizarra E