The activating effect of fatty acid on the mitochondrial uncoupling protein reconstituted in liposomes

The valinomycin-induced H+ uptake in liposomes with reconstituted uncoupling protein from brown adipose tissue mitochondria is greatly enhanced when palmitic acid (4-20 micrograms/mg lipid) is incorporated prior to proteoliposome preparation. This procedure does not change basal H+ permeability of the liposomes. H+ uptake in proteoliposomes is inhibited by GDP, the net GDP-sensitive H+ flux being higher when palmitic acid was incorporated than in its absence. The net palmitate-induced increment of H+ uptake decreases with increasing concentration of GDP. These results suggest that palmitate augments H+ flux via the uncoupling protein and that direct interaction of palmitate with the uncoupling protein occurs during such activation within the hydrophobic core of the membrane.