Many respiratory-chain enzymes convert lipophilic quinones, like co-enzyme Q in the mitochondrial membrane. As these quinones are not water-soluble, they are experimentally difficult to handle, and many enzyme assays use water-soluble quinone analogues instead. We have developed an electrochemical system in which a lipid membrane is either ‘tethered’ or adsorbed to an electrode and the native quinone-pool is electrochemically reduced or oxidised. Enzyme turn-over is conveniently monitored as an electrochemical current and the action of enzyme substrates and inhibitors can thus be directly measured. By adsorbing intact proteoliposomes on a surface, it is also possible to simultaneously measure proton transport is in fluorescence microscopy.

Cytochrome bd as an antibacterial target

Ever since the FDA approved the drug bedaquiline, which inhibits the activity the F₀F₁-ATP synthase, for the treatment of tuberculosis in 2012, respiratory-chain enzymes have been an active target space for the discovery of new antibiotics. Bacterial cytochrome bd, which is a terminal oxidase, has been of special interest as there is no human homologue of this in enzyme in mitochondria. Cytochrome bd oxidises the quinone pool in a variety of bacterial species, typically under oxygen limiting conditions. Using our membrane-modified electrodes, we are studying the interaction cytochrome bd with the quinone pool. 

Key publications

Nakatani Y., Shimaki Y., Dutta D., Muench S.P., Ireton K., Cook G.M. & Jeuken L.J.C. (2019), Unprecedented Properties of Phenothiazines Unraveled by a NDH-2 Bioelectrochemical Assay Platform, Journal of the American Chemical Society 142: 1311-1320. DOI: 10.1021/jacs.9b10254

Heath G.R., Li M., Rong H., Radu V., Frielingsdorf S., Lenz O., Butt J.N. & Jeuken L.J.C. (2017), Multilayered Lipid Membrane Stacks for Biocatalysis Using Membrane Enzymes, Advanced Functional Materials 27: 1606265. DOI: 10.1002/adfm.201606265

Li M. Jørgensen S.K. McMillan D.G.G. Krzemiński Ł. Daskalakis N.N. Partanen R.H. Tutkus M. Tuma R. Stamou D. Hatzakis N.S. Jeuken L.J.C. (2015), Single Enzyme Experiments Reveal a Long-Lifetime Proton Leak State in a Heme-Copper Oxidase, Journal of the American Chemical Society 137: 16055-16063. DOI: 10.1021/jacs.5b08798

Radu V., Frielingsdorf S., Evans S.D., Lenz O. & Jeuken L.J.C. (2014), Enhanced Oxygen-Tolerance of the Full Heterotrimeric Membrane-Bound [NiFe]-Hydrogenase of Ralstonia eutropha, Journal of the American Chemical Society 136: 8512-8515. DOI: 10.1021/ja503138p