A SIMPLE LIGHT-DRIVEN TRANSMEMBRANE PROTON PUMP

Light-induced lipophilic porphyrin/aqueous acceptor charge separation across a single lipid-water interface can pump protons across the lipi d bilayer when the hydrophobic weak acids, carbonylcyanide m-chlorophe nylhydrazone and its p-trifluoromethoxyphenyl analogue, are present, T hese compounds act as proton carriers across lipid bilayers, In their symmetric presence across the bilayer, the positive currents and volta ges produced by the photogeneration of porphyrin cations are replaced by larger negative currents and voltages. The maximum negative current and voltage occur at the pH of maximum dark conductance. The reversed larger current and voltage show a positive ionic charge transport in the same direction as the electron transfer, This transport can form a n ion concentration gradient, The movement of protons is verified by a n unusual D2O isotope effect that increases the negative ionic current by 2- to 3-fold, These effects suggest that an interfacial pK shift o f the weak acid caused by the local electric field of photoformed porp hyrin cations/acceptor anions functions as the driving force, The esti mated pumping efficiency is 10-30%. Time-resolved results show that pr oton pumping across the bilayer occurs on the millisecond time scale, similar to that of biological pumps. This light-driven proteinless pum p offers a simple model for a prebiological energy transducer.