An Artificial Photosynthetic Membrane

In bacteria, photosynthesis involves absorption of light by antenna systems and transfer of excitation to reaction centers, which convert the excitation energy to electrochemical potential energy in the form of transmembrane charge separation. A proton-pumping protein uses this stored energy to generate proton motive force across the membrane, which in turn drives the synthesis of adenosine triphosphate (ATP). All of these steps can now be mimicked in the laboratory. Artificial reaction centers can be prepared from porphyrins and other chromophores, electron donors, and electron acceptors linked by covalent bonds. Suitable artificial reaction centers can be vectorially inserted into the lipid bilayers of liposomes, where they function as constituents of transmembrane light-driven proton pumps. Finally, the proton motive force produced can be used to synthesize ATP via catalysis by F0F,-ATP synthase isolated from chloroplasts. The synthetic and natural systems can use light energy to produce ATP at comparable chemical potentials.