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Query: KEGG:D02011 (FAD)
 5,530 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Two groups have now published sequences of the six genes contained in the operon coding for the sodium-linked NADH-ubiquinone oxidoreductase of Vibrio alginolyticus. Sequence analyses indicate that this enzyme is unrelated to other known respiratory NADH dehydrogenases. A search for cofactor motifs suggests that the enzyme contains only one FAD, a ferredoxin-type iron sulphur centre, and the NADH-binding site. These are all located on NqrF, a subunit that can be recognized as a new member of a large diverse family of NAD(P)H-oxidizing flavoenzymes. A possible model of ion-coupling is presented, based upon this new information.
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PMID:Predicted structure and possible ionmotive mechanism of the sodium-linked NADH-ubiquinone oxidoreductase of Vibrio alginolyticus. 749 78

The Na(+)-pumping NADH-ubiquinone oxidoreductase has six polypeptide subunits (NqrA-F) and a number of redox cofactors, including a noncovalently bound FAD and a 2Fe-2S center in subunit F, covalently bound FMNs in subunits B and C, and a noncovalently bound riboflavin in an undisclosed location. The FMN cofactors in subunits B and C are bound to threonine residues by phosphoester linkages. A neutral flavin-semiquinone radical is observed in the oxidized enzyme, whereas an anionic flavin-semiquinone has been reported in the reduced enzyme. For this work, we have altered the binding ligands of the FMNs in subunits B and C by replacing the threonine ligands with other amino acids, and we studied the resulting mutants by EPR and electron nuclear double resonance spectroscopy. We conclude that the sodium-translocating NADH:quinone oxidoreductase forms three spectroscopically distinct flavin radicals as follows: 1) a neutral radical in the oxidized enzyme, which is observed in all of the mutants and most likely arises from the riboflavin; 2) an anionic radical observed in the fully reduced enzyme, which is present in wild type, and the NqrC-T225Y mutant but not the NqrB-T236Y mutant; 3) a second anionic radical, seen primarily under weakly reducing conditions, which is present in wild type, and the NqrB-T236Y mutant but not the NqrC-T225Y mutant. Thus, we can tentatively assign the first anionic radical to the FMN in subunit B and the second to the FMN in subunit C. The second anionic radical has not been reported previously. In electron nuclear double resonance spectra, it exhibits a larger line width and larger 8alpha-methyl proton splittings, compared with the first anionic radical.
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PMID:A new flavin radical signal in the Na(+)-pumping NADH:quinone oxidoreductase from Vibrio cholerae. An EPR/electron nuclear double resonance investigation of the role of the covalently bound flavins in subunits B and C. 1697 19