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Type of publication: Journal Article
Type of document: Full Paper

Year: 2003

Authors: Urbánková, E; Voltchenko, A; Pohl, P; Jezek, P; Pohl, EE

Title: Transport kinetics of uncoupling proteins. Analysis of UCP1 reconstituted in planar lipid bilayers.

Source: J Biol Chem. 2003; 278(35):32497-32500

Authors Vetmeduni Vienna:

Pohl Elena

According to alternative hypotheses, mitochondrial uncoupling protein 1 (UCP1) is either a proton channel ("buffering model") or a fatty acid anion carrier ("fatty acid cycling"). Transport across the proton channel along a chain of hydrogen bonds (Grotthus mechanism) may include fatty acid carboxyl groups or occur in the absence of fatty acids. In this work, we demonstrate that planar bilayers reconstituted with UCP1 exhibit an increase in membrane conductivity exclusively in the presence of fatty acids. Hence, we can exclude the hypothesis considering a preexisting H+ channel in UCP1, which does not require fatty acid for function. The augmented conductivity is nearly completely blocked by ATP. Direct application of transmembrane voltage and precise current measurements allowed determination of ATP-sensitive conductances at 0 and 150 mV as 11.5 and 54.3 pS, respectively, by reconstituting nearly 3 x 10(5) copies of UCP1. The proton conductivity measurements carried out in presence of a pH gradient (0.4 units) allowed estimation of proton turnover numbers per UCP1 molecule. The observed transport rate of 14 s-1 is compatible both with carrier and channel nature of UCP1.

Keywords Pubmed: Adenosine Triphosphate/metabolism
Carrier Proteins/chemistry*
Carrier Proteins/metabolism
Carrier Proteins/physiology*
Dose-Response Relationship, Drug
Fatty Acids/metabolism*
Hydrogen Bonding
Hydrogen-Ion Concentration
Ion Channels
Lipid Bilayers/metabolism*
Membrane Potentials
Membrane Proteins/chemistry*
Membrane Proteins/metabolism
Membrane Proteins/physiology*
Mitochondrial Proteins
Oleic Acid/pharmacology
Protein Transport

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