Question

4. Define uncoupling proteins (UCPs) and describe what is their effect in the mitochondrial electrochemical gradient.

Answer 1

The uncoupling proteins (UCPs) are a class of proteins found in the inner mitochondrial membrane and compete with the F₀F₁-ATP synthase for the proton electron gradient built up by the activity of respiratory-chain Complexes I, III, and IV. In mitochondria, the electrochemical gradient created by the pumping of protons by complex I, III, and IV drives the synthesis of ATP through F₀F₁-ATP synthase. The uncoupler proteins (UCPs), however, create a shunt by carrying protons themselves instead of letting it pass through ATP synthase. This leads to dissipation of electrochemical gradient in the mitochondria. Activation of UCPs enhances respiration, and the uncoupling process results in a futile cycle and dissipation of oxidation energy as heat. This energy-dissipatory mechanism can serve functions such as thermogenesis, maintenance of the redox balance, or reduction in the production of reactive oxygen species.