Identification of six subunits constituting Na+-translocating NADH-quinone reductase from the marine Vibrio alginolyticus.

We previously reported that the purified Na+-translocating NADH-quinone reductase (NQR) from the marine Vibrio alginolyticus is composed of three major subunits, alpha, beta and gamma. NQR operon was sequenced and was found to be composed of 6 structural genes. Among these genes, nqr1, nqr3 and nqr6 were identified to code for alpha-, gamma- and beta-subunits, respectively. The protein products from nqr2, nqr4 and nqr5, however, were not reported. The sequence data predicted that these three proteins are very hydrophobic and may be unusual in mobility and staining on SDS-PAGE. By modifying the detection method of proteins on SDS-PAGE, we could detect all six subunits encoded by NQR operon in the purified NQR complex. The open reading frame of each subunit was identified from its N-terminal amino acid sequence.