title: The molecular mechanism of action of the proton ionophore FCCP (carbonylcyanide p-trifluoromethoxyphenylhydrazone).
abstract: We propose a simple model that accounts for the ability of the weak acid FCCP (Carbonylcyanide-p-trifluoromethoxyphenylhydrazone) to both transport protons across phospholipid bilayer membranes and uncouple oxidation from phosphorylation in mitochondria. Four parameters are required to characterize this model: the rate constant for the movement of A- across the membrane, kA, the rate constant for the movement of HA across the membrane, kHA, the adsorption coefficient of A- onto the membrane-solution interface, beta A, and the surface pK. These four parameters were determined from kinetic measurements on planar bilayer membranes using the charge-pulse and voltage-clamp techniques. We confirmed the adequacy of the model by determining each of these parameters independently, utilizing equilibrium dialysis, zeta potential, membrane potential, spectrophotometric, and conductance measurements. For a phosphatidylethanolamine bilayer the values of the parameters are kHA = 10(4)S-1, beta A = 3 10(-3) cm, and 6.0 less than pK less than 6.4. As predicted theoretically, the value of KA depends on both the applied voltage, V, and dielectric constant of the membrane, epsilon r; when V approaches zero and the membrane contains chlorodecane (epsilon r congruent to 2.7) kA = 700 s-1. If oxidation is coupled to phosphorylation by means of a delta microH+, and V er congruent to 2.7 for the inner membrane of the mitochondrion, the model predicts that FCCP should exert maximal uncoupling activity at a pH congruent to  pK. This prediction agrees with the published experimental results.
mesh_terms: D002259:Carbonyl Cyanide p-Trifluoromethoxyphenylhydrazone / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008051:Lipid Bilayers; D008433:Mathematics; D008564:Membrane Potentials / Q000187:drug effects; D008928:Mitochondria / Q000187:drug effects / Q000378:metabolism; D008954:Models, Biological; D009570:Nitriles / Q000494:pharmacology; D010085:Oxidative Phosphorylation / Q000187:drug effects; D010713:Phosphatidylcholines; D010714:Phosphatidylethanolamines; D013816:Thermodynamics
chemical_list: D008051:Lipid Bilayers; D009570:Nitriles; D010713:Phosphatidylcholines; D010714:Phosphatidylethanolamines; C021016:1,2-diphytanoylphosphatidylcholine; D002259:Carbonyl Cyanide p-Trifluoromethoxyphenylhydrazone