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Inhibition of proton-transfer steps in transhydrogenase by transition metal ions

Whitehead, SJ; Iwaki, M; Cotton, NPJ; Rich, PR; Jackson, JB; (2009) Inhibition of proton-transfer steps in transhydrogenase by transition metal ions. BBA-BIOENERGETICS , 1787 (10) 1276 - 1288. 10.1016/j.bbabio.2009.06.001.

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Abstract

Transhydrogenase couples proton translocation across a bacterial or mitochondrial membrane to the redox reaction between NAD(H) and NADP(H). Purified intact transhydrogenase from Escherichia coli was prepared, and its His tag removed. The forward and reverse transhydrogenation reactions catalysed by the enzyme were inhibited by certain metal ions but a "cyclic reaction" was stimulated. Of metal ions tested they were effective in the order Pb2+>Cu2+>Zn2+ = Cd2+>Ni2+>Co2+. The results suggest that the metal ions affect transhydrogenase by binding to a site in the proton-transfer pathway. Attenuated total-reflectance Fourier-transform infrared difference spectroscopy indicated the involvement of His and Asp/Glu residues in the Zn2+-binding site(s). A mutant in which beta His91 in the membrane-spanning domain of transhydrogenase was replaced by Lys had enzyme activities resembling those of wild-type enzyme treated with Zn2+. Effects of the metal ion on the mutant were much diminished but still evident. Signals in Zn2+-induced FTIR difference spectra of the beta His91 Lys mutant were also attributable to changes in His and Asp/Glu residues but were much smaller than those in wild-type spectra. The results support the view that beta His91 and nearby Asp or Glu residues participate in the proton-transfer pathway of transhydrogenase. (C) 2009 Elsevier B.V. All rights reserved.

Type: Article
Title: Inhibition of proton-transfer steps in transhydrogenase by transition metal ions
DOI: 10.1016/j.bbabio.2009.06.001
Keywords: Transhydrogenase, Membrane protein, Zinc ion, Proton translocation, Redox, FTIR, NICOTINAMIDE NUCLEOTIDE TRANSHYDROGENASE, CYTOCHROME-C-OXIDASE, ESCHERICHIA-COLI TRANSHYDROGENASE, NADP(H)-BINDING COMPONENT DIII, BACTERIAL REACTION CENTERS, BOVINE HEART-MITOCHONDRIA, TRANSLOCATING TRANSHYDROGENASE, HYDRIDE TRANSFER, RHODOSPIRILLUM-RUBRUM, ADENINE-DINUCLEOTIDE
UCL classification: UCL > Provost and Vice Provost Offices
UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences
UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences > Faculty of Life Sciences
UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences > Faculty of Life Sciences > Div of Biosciences
UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences > Faculty of Life Sciences > Div of Biosciences > Structural and Molecular Biology
URI: http://discovery.ucl.ac.uk/id/eprint/65900
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