title: Occurrence of a bound ubiquinone and its function in Escherichia coli membrane-bound quinoprotein glucose dehydrogenase.
abstract: The membrane-bound pyrroloquinoline quinone (PQQ)-containing quinoprotein glucose dehydrogenase (mGDH) in Escherichia coli functions by catalyzing glucose oxidation in the periplasm and by transferring electrons directly to ubiquinone (UQ) in the respiratory chain. To clarify the intramolecular electron transfer of mGDH, quantitation and identification of UQ were performed, indicating that purified mGDH contains a tightly bound UQ(8) in its molecule. A significant increase in the EPR signal was observed following glucose addition in mGDH reconstituted with PQQ and Mg(2+), suggesting that bound UQ(8) accepts a single electron from PQQH(2) to generate semiquinone radicals. No such increase in the EPR signal was observed in UQ(8)-free mGDH under the same conditions. Moreover, a UQ(2) reductase assay with a UQ-related inhibitor (C49) revealed different inhibition kinetics between the wild-type mGDH and UQ(8)-free mGDH. From these findings, we propose that the native mGDH bears two ubiquinone-binding sites, one (Q(I)) for bound UQ(8) in its molecule and the other (Q(II)) for UQ(8) in the ubiquinone pool, and that the bound UQ(8) in the Q(I) site acts as a single electron mediator in the intramolecular electron transfer in mGDH.
authors: Department of Biological Chemistry, Faculty of Agriculture, Yamaguchi University, Yamaguchi 753-8515, Japan.
authors: M D
authors: MD
authors: Elias
authors: Satsuki
authors: S
authors: Nakamura
authors: Catharina T
authors: CT
authors: Migita
authors: Hideto
authors: H
authors: Miyoshi
authors: Hirohide
authors: H
authors: Toyama
authors: Kazunobu
authors: K
authors: Matsushita
authors: Osao
authors: O
authors: Adachi
authors: Mamoru
authors: M
authors: Yamada
mesh_terms: D002462:Cell Membrane / Q000737:chemistry / Q000378:metabolism; D004579:Electron Transport; D004926:Escherichia coli / Q000737:chemistry / Q000378:metabolism*; D005948:Glucose Dehydrogenases / Q000737:chemistry / Q000378:metabolism*; D011485:Protein Binding; D014451:Ubiquinone / Q000737:chemistry / Q000378:metabolism*
chemical_list: D014451:Ubiquinone; D005948:Glucose Dehydrogenases; C033955:glucose dehydrogenase (pyrroloquinoline-quinone)