Recent progress in the Na+-translocating NADH-quinone reductase from the marine Vibrio alginolyticus

The respiratory chain of Cram-negative marine and halophilic bacteria has a Na+-dependent NADH-quinone reductase that functions as a primary Na+ pump. The Na+-translocating NADH-quinone reductase (NQR) from the marine Vibrio alginolyticus is composed of six structural genes (nqrA to nqrF). The NqrF subunit has non-covalently bound FAD. There are conflicting results on the existence of other flavin cofactors. Recent studies revealed that the NqrB and NqrC subunits have a covalently bound flavin, possibly FMN, which is attached to a specified threonine residue. A novel antibiotic, korormicin, was found to specifically inhibit the NQR complex. From the homology search of the nqr operon, it was found that the Na+-pumping NQR complex is widely distributed among Gram-negative pathogenic bacteria. (C) 2001 Elsevier Science B.V. All rights reserved.