The origin of the sodium‐dependent NADH oxidation by the respiratory chain of Klebsiella pneumoniae

Properties of Klebsiella pneumoniae respiratory chain enzymes catalyzing NADH oxidation have been studied. Using constructed K. pneumoniae mutant strains, it was shown that three enzymes belonging to different families of NADH:quinone oxidoreductases operate in this bacterium. The NDH-2-type enzyme is not coupled with energy conservation, the NDH-1-type enzyme is a primary proton pump, and the NQR-type enzyme is homologous to the sodium-motive NADH dehydrogenase of Vibrio and is shown to be a primary Na(+) pump. It is concluded that the NQR-type enzyme, not the NDH-1-type enzyme, catalyzes sodium-dependent NADH oxidation in K. pneumoniae.