| Research Abstract |
Earlier studies in this laboratory demonstrated that the NaィイD1+ィエD1-translocating NADH-quinone reductase (NQR) of the marine bacterium Vibrio alginolyticus is composed of 6 structural genes. In this studies, 6 subunits corresponding to Nqr1, Nqr2, Nqr3, Nqr4, Nqr5 and Nqr6 could be detected on SDS-PAGE by modifying the detection method of proteins. The open reading frame of each subunit was identified from its N-terminal amino acid sequence. The genetic defect of a mutant Nap1 was found to be caused by the insertion of a 1.2kbp DNA fragment into the C-terminal region of nqr6 gene. We dissociated the purified NQR complex to subunit components, Nqr1, Nqr3, Nqr6 and Nqr2,4,5. The latter Nqr2,4,5 fraction contained all hydrophobic subunits and this fraction was difficult to further dissociate into each component subunit. We could construct a reconstitution system starting from these subunits, and it was found that all six subunits are essential for the NQR activity. Recently, a novel antibiotic, korormicin, was found to specifically inhibit NQR activity. The mode of korormicin inhibition was purely nonncompetitive for Q-1 with the inhibitor constant of 82 pM. The site of korormicin binding was partially overlapped with that of HQNO.
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