Effect of carbonylcyanide-4-(trifluoromethoxy)phenylhydrazone (FCCP) on the interaction of 1-anilino-8-naphthalene sulfonate (ANS) with phosphatidylcholine liposomes

The weak hydrophobic acid carbonylcyanide-4-(trifluoromethoxy)phenylhydrazone (FCCP) is a protonophoric uncoupler of oxidative phosphorylation in mitochondria. It dissipates the electrochemical proton gradient (Delta mu(H) (+)) increasing the mitochondrial oxygen consumption. However, at concentrations higher than 1 mu M it exhibits additional effects on mitochondrial energy metabolism, which were tentatively related to modifications of electrical properties of the membrane. Here we describe the effect of FCCP on the binding of 1-anilino-8-naphthalene sulfonate (ANS) to 1, 2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) and 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) unilamellar vesicles. FCCP inhibited the binding of ANS to liposomes either in the gel or in the liquid crystalline phase, by increasing the apparent dissociation constant of ANS. Smaller effect on the dissociation constant was observed at high ionic strength, suggesting that the effect of FCCP is through modification of the electrostatic properties of the membrane interface. In addition, FCCP also decreased (approximately 50 %) the quantum yield and increased the intrinsic dissociation constant of membrane-bound ANS, results that suggest that FCCP makes the environment of the ANS binding sites more polar. On those grounds we postulate that the binding of FCCP: i) increases the density of negative charges in the membrane surface; and ii) distorts the phospholipid bilayer, increasing the mobility of the polar headgroups making the ANS binding site more accessible to water.