title: Reduction of cytochrome c oxidase by a second electron leads to proton translocation.
abstract: Cytochrome c oxidase, the terminal enzyme of cellular respiration in mitochondria and many bacteria, reduces O(2) to water. This four-electron reduction process is coupled to translocation (pumping) of four protons across the mitochondrial or bacterial membrane; however, proton pumping is poorly understood. Proton pumping was thought to be linked exclusively to the oxidative phase, that is, to the transfer of the third and fourth electron. Upon re-evaluation of these data, however, this proposal has been questioned, and a transport mechanism including proton pumping in the reductive phase--that is, during the transfer of the first two electrons--was suggested. Subsequently, additional studies reported that proton pumping during the reductive phase can occur, but only when it is immediately preceded by an oxidative phase. To help clarify the issue we have measured the generation of the electric potential across the membrane, starting from a defined one-electron reduced state. Here we show that a second electron transfer into the enzyme leads to charge translocation corresponding to pumping of one proton without necessity for a preceding turnover.
authors: Department of Biophysical Chemistry, Max-Planck-Institut für Biophysik, Kennedyallee 70, D-60596 Frankfurt/Main, Germany.
authors: Maarten
authors: M
authors: Ruitenberg
authors: Aimo
authors: A
authors: Kannt
authors: Ernst
authors: E
authors: Bamberg
authors: Klaus
authors: K
authors: Fendler
authors: Hartmut
authors: H
authors: Michel
mesh_terms: D001692:Biological Transport; D002384:Catalysis; D019069:Cell Respiration; D003576:Electron Transport Complex IV / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D004583:Electrons; D008081:Liposomes / Q000737:chemistry / Q000378:metabolism*; D008564:Membrane Potentials; D008958:Models, Molecular; D009154:Mutation; D010084:Oxidation-Reduction; D010100:Oxygen / Q000378:metabolism; D010231:Paracoccus denitrificans / Q000201:enzymology* / Q000378:metabolism; D010782:Photolysis; D011487:Protein Conformation; D011510:Proteolipids / Q000378:metabolism; D011522:Protons; D013997:Time Factors; D014867:Water / Q000378:metabolism
chemical_list: D008081:Liposomes; D011510:Proteolipids; D011522:Protons; C020485:proteoliposomes; D014867:Water; D003576:Electron Transport Complex IV; D010100:Oxygen