Single Enzyme Experiments Reveal a Long-Lifetime Proton Leak State in a Heme-Copper Oxidase

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• 作者：Mengqiu Li ; Sune K. J?rgensen ; Duncan G. G. McMillan ; ?ukasz Krzemiński ; Nikolaos N. Daskalakis ; Riitta H. Partanen ; Marijonas Tutkus ; Roman Tuma ; Dimitrios Stamou ; Nikos S. Hatzakis ; Lars J. C. Jeuken
• 刊名：Journal of the American Chemical Society
• 出版年：2015
• 出版时间：December 30, 2015
• 年：2015
• 卷：137
• 期：51
• 页码：16055-16063
• 全文大小：437K
• ISSN：1520-5126

文摘

Heme-copper oxidases (HCOs) are key enzymes in prokaryotes and eukaryotes for energy production during aerobic respiration. They catalyze the reduction of the terminal electron acceptor, oxygen, and utilize the Gibbs free energy to transport protons across a membrane to generate a proton (ΔpH) and electrochemical gradient termed proton motive force (PMF), which provides the driving force for the adenosine triphosphate (ATP) synthesis. Excessive PMF is known to limit the turnover of HCOs, but the molecular mechanism of this regulatory feedback remains relatively unexplored. Here we present a single-enzyme study that reveals that cytochrome bo₃ from Escherichia coli, an HCO closely homologous to Complex IV in human mitochondria, can enter a rare, long-lifetime leak state during which proton flow is reversed. The probability of entering the leak state is increased at higher ΔpH. By rapidly dissipating the PMF, we propose that this leak state may enable cytochrome bo₃, and possibly other HCOs, to maintain a suitable ΔpH under extreme redox conditions.