Existence of Na+-translocating NADH-quinone reductase in Haemophilus influenzae.

We previously cloned and sequenced nqr operon encoding the Na+-translocating NADH-quinone reductase (NQR) from the marine bacterium Vibrio alginolyticus. A gene cluster very similar to nqr operon was found to exist in the genome of Haemophilus influenzae Rd. We examined the membrane fraction from H. influenzae, and the respiratory chain of H. influenzae was found to contain a Na+-dependent NQR that is essentially identical to those found in the marine V. alginolyticus. These results indicate that quite similar to the salt-loving marine bacteria, the blood-loving H. influenzae has a redox-driven Na+ pump and utilizes Na+ circulation for energy coupling.