The Na+-Translocating NADH:quinone Oxidoreductase (NDH I) from Klebsiella pneumoniae and Escherichia coli: Implications for the Mechanism of Redox-Driven Cation Translocation by Complex I

Eukaryotic complex I integrated into the respiratory chain transports at least 4 H+ per NADH oxidized. Recent results indicate that the cation selectivity is altered to Na+ in complex I (NDH I) isolated from the enterobacteria Escherichia coli and Klebsiella pneumoniae. A sequence analysis illustrates the characteristic differences of the enterobacterial, Na+-translocating NDH I compared to the H+-translocating complex I from mitochondria. Special attention is given to the membranous NuoL (ND5, Nqo12) subunits that possess striking sequence similarities to secondary Na+/H+ antiporters and are proposed to participate in Na+ transport. A model of redox-linked Na+ (or H+) transport by complex I is discussed based on the ion-pair formation of a negatively charged ubisemiquinone anion with a positively charged Na+ (or H+).