PMID:14970214
| Citation |
Stolpe, S and Friedrich, T (2004) The Escherichia coli NADH:ubiquinone oxidoreductase (complex I) is a primary proton pump but may be capable of secondary sodium antiport. J. Biol. Chem. 279:18377-83 |
|---|---|
| Abstract |
The NADH:ubiquinone oxidoreductase (complex I) couples the transfer of electrons from NADH to ubiquinone with the translocation of protons across the membrane. Recently, it was demonstrated that complex I from Klebsiella pneumoniae translocates sodium ions instead of protons. Experimental evidence suggested that complex I from the close relative Escherichia coli works as a primary sodium pump as well. However, data obtained with whole cells showed the presence of an NADH-induced electrochemical proton gradient. In addition, Fourier transform IR spectroscopy demonstrated that the redox reaction of the E. coli complex I is coupled to a protonation of amino acids. To resolve this contradiction we measured the properties of isolated E. coli complex I reconstituted in phospholipids. We found that the NADH:ubiquinone oxidoreductase activity did not depend on the sodium concentration. The redox reaction of the complex in proteoliposomes caused a membrane potential due to an electrochemical proton gradient as measured with fluorescent probes. The signals were sensitive to the protonophore carbonyl cyanide m-chlorophenylhydrazone (CCCP), the inhibitors piericidin A, dicyclohexylcarbodi-imide (DCCD), and amiloride derivatives, but were insensitive to the sodium ionophore ETH-157. Furthermore, monensin acting as a Na(+)/H(+) exchanger prevented the generation of a proton gradient. Thus, our data demonstrated that the E. coli complex I is a primary electrogenic proton pump. However, the magnitude of the pH gradient depended on the sodium concentration. The capability of complex I for secondary Na(+)/H(+) antiport is discussed. |
| Links |
PubMed Online version:10.1074/jbc.M311242200 |
| Keywords |
Amino Acids/metabolism; Electron Transport Complex I/physiology; Escherichia coli Proteins/physiology; Fluorescent Dyes; Fluorometry; Hydrogen-Ion Concentration; Liposomes; Membrane Potentials; Oxidation-Reduction; Proton Pumps; Sodium/pharmacology; Sodium-Hydrogen Antiporter |
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