Uncoupling proteins outside the animal and plant kingdoms: functional and evolutionary aspects

The appearance of intracellular oxidative phosphorylation at the time of acquisition of mitochondria in Eukarya was very soon accompanied by the emergence of uncoupling protein, a carrier specialized in Fred fatty acid-mediated H+ recycling that can modulate the tightness 4 coupling between mitochondrial respiration and ATP synthesis, thereby maintaining a balance between energy supply and demand in the cell and defending cells against damaging reactive oxygen species production when electron carriers of the respiratory chain become overreduced. The simultaneous occurrence of redox free energy-dissipating oxidase, which has the same final effect, could be related to the functional interactions between both dissipative systems. (C) 2002 Federation of European Biochemical Societies. Published by Elsevier Science B.V. All rights reserved.