NDUFS4, also known as NADH dehydrogenase (ubiquinone) Fe-S protein 4, is an accessory subunit of the mitochondrial membrane respiratory chain NADH dehydrogenase (Complex I), the first multi-subunit enzyme complex of the mitochondrial respiratory chain. Complex I plays a vital role in cellular ATP production, the primary source of energy for many crucial processes in living cells. It removes electrons from NADH and passes them by a series of different protein-coupled redox centers to the electron acceptor ubiquinone. Recombinant human NDUFS4 protein was expressed in E. coli and purified by using conventional chromatography. Alternative Names: NADH dehydrogenase protein, Complex I 18 kDa protein, NDUFS4, NADH ubiquinone oxidoreductase 18 kDa subunit., Complex I AQDQ protein, NDUFS-4, NDUFS-4 protein, NADH dehydrogenase (ubiquinone) Fe-S protein 4 protein, mitochondrial respiratory chain complex I (18 KD subunit) protein, AQDQ protein, NDUFS 4 protein, NDUFS 4, CI AQDQ protein, NADH dehydrogenase (ubiquinone) Fe-S protein 4 CI 18 kDa protein