title: Inhibition of Escherichia coli respiratory complex I by Zn(2+).
abstract: The energy-converting NADH:ubiquinone oxidoreductase, respiratory complex I, couples NADH oxidation and quinone reduction with the translocation of protons across the membrane. Complex I exhibits a unique L shape with a peripheral arm extending in the aqueous phase and a membrane arm embedded in the lipid bilayer. Both arms have a length of ∼180 Å. The electron transfer reaction is catalyzed by a series of cofactors in the peripheral arm, while the membrane arm catalyzes proton translocation. We used the inhibition of complex I by zinc to shed light on the coupling of the two processes, which is not yet understood. Enzyme kinetics revealed the presence of two high-affinity binding sites for Zn(2+) that are attributed to the proton translocation pathways in the membrane arm. Electrochemically induced Fourier transform infrared difference spectroscopy demonstrated that zinc binding involves at least two protonated acidic residues. Electron paramagnetic resonance spectroscopy showed that one of the cofactors is only partially reduced by NADH in the presence of Zn(2+). We conclude that blocking the proton channels in the membrane arm leads to a partial block of the electron transfer in the peripheral arm, indicating the long-range coupling between both processes.
authors.affiliation: Institut für Biochemie, Albert-Ludwigs-Universität , 79104 Freiburg, Germany.
authors.forename: Marius
authors.initials: M
authors.lastname: Schulte
authors.forename: Dinah
authors.initials: D
authors.lastname: Mattay
authors.forename: Sebastien
authors.initials: S
authors.lastname: Kriegel
authors.forename: Petra
authors.initials: P
authors.lastname: Hellwig
authors.forename: Thorsten
authors.initials: T
authors.lastname: Friedrich
mesh_terms: D020134:Catalytic Domain; D004579:Electron Transport; D042967:Electron Transport Complex I / Q000037:antagonists & inhibitors* / Q000737:chemistry; D004791:Enzyme Inhibitors / Q000737:chemistry*; D004926:Escherichia coli / Q000201:enzymology*; D029968:Escherichia coli Proteins / Q000037:antagonists & inhibitors* / Q000737:chemistry; D007700:Kinetics; D009243:NAD / Q000737:chemistry; D010084:Oxidation-Reduction; D011485:Protein Binding; D017975:Ruthenium Compounds / Q000737:chemistry; D015032:Zinc / Q000737:chemistry*
chemical_list: D004791:Enzyme Inhibitors; D029968:Escherichia coli Proteins; D017975:Ruthenium Compounds; D009243:NAD; C031584:hexammineruthenium; D042967:Electron Transport Complex I; D015032:Zinc