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Polyunsaturated fatty acids activate human uncoupling proteins 1 and 2 in planar lipid bilayers

Valeri Beck^*, Martin Jabrek, Tatiana Demina^*,1, Anne Rupprecht^*, Richard K. Porter, Petr Jeek and Elena E. Pohl^*,2

^* Institute of Cell Biology and Neurobiology, Centre for Anatomy, Charité Universitätsmedizin, Berlin, Germany;

Department of Membrane Transport Biophysics, Institute of Physiology, Academy of Sciences of the Czech Republic, Prague, Czech Republic; and

School of Biochemistry and Immunology, Trinity College Dublin, Dublin, Ireland

²Correspondence: Institute of Cell Biology and Neurobiology, Charité Universitätsmedizin, Charitéplatz 1, 10117 Berlin, Germany. E-mail: elena.pohl{at}charite.de

Uncoupling proteins 1 (UCP1) and 2 (UCP2) belong to the family of mitochondrial anion transporters and share 59% sequence identity with each other. Whereas UCP1 was shown to be responsible for the rapid production of heat in brown adipose tissue, the primary function and transport properties of ubiquitously expressed UCP2 are controversially discussed. Here, for the first time, the activation pattern of the recombinant human UCP2 in comparison to the recombinant human UCP1 are studied using a well-defined system of planar lipid bilayers. It is shown that despite apparently different physiological functions, hUCP2 exhibited its protonophoric function similar to hUCP1—exclusively in the presence of long-chain fatty acids (FA). The calculated hUCP2 transport rate of 4.5 s^–1 is the same order of magnitude, as shown previously for UCP1. It leads to the conclusion that the differences in the activity of both proteins in living mitochondria are based exclusively on their different expression level. Both proteins are activated much more effectively by polyunsaturated than by saturated FA. The proton and total membrane conductances increased in the range palmitic < oleic < eicosatrienoic < linoleic < retinoic < arachidonic acids. The higher uncoupling protein (UCP)—dependent conductance in the presence of polyunsaturated FA is explained on the basis of the FA cycling hypothesis.—Beck, V., Jabrek, M., Demina, T., Rupprecht, A., Porter, R. K., Jeek, P., Pohl, E. E. Polyunsaturated fatty acids activate human uncoupling proteins 1 and 2 in planar lipid bilayers.

Key Words: mitochondria • anion transporter • proton transport • artificial bilayer membranes • reactive oxygen species

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