LIGHT-DRIVEN PRODUCTION OF ATP CATALYZED BY F0F1-ATP SYNTHASE IN AN ARTIFICIAL PHOTOSYNTHETIC MEMBRANE

Energy-transducing membranes of living organisms couple spontaneous to non-spontaneous processes through the intermediacy of protonmotive fo rce (p.m.f.)-an imbalance in electrochemical potential of protons acro ss the membrane, In most organisms, p.m.f. is generated by redox react ions that are either photochemically driven, such as those in photosyn thetic reaction centres, or intrinsically spontaneous, such as those o f oxidative phosphorylation in mitochondria. Transmembrane proteins (s uch as the cytochromes and complexes I, III and IV in the electron-tra nsport chain in the inner mitochondrial membrane) couple the redox rea ctions to proton translocation, thereby conserving a fraction of the r edox chemical potential as p.m.f. Many transducer proteins couple p.m. f. to the performance of biochemical work, such as biochemical synthes is and mechanical and transport processes, Recently, an artificial pho tosynthetic membrane was reported in which a photocyclic process was u sed to transport protons across a liposomal membrane, resulting in aci dification of the Liposome's internal volume(1), If significant p.m.f. is generated in this system, then incorporating an appropriate transd ucer into the liposomal bilayer should make it possible to drive a non -spontaneous chemical process, Here we report the incorporation of F0F 1-ATP synthase into liposomes containing the components of the proton- pumping photocycle, Irradiation of this artificial membrane,vith visib le Light results in the uncoupler-and inhibitor-sensitive synthesis of adenosine triphosphate (ATP) against an ATP chemical potential of sim ilar to 12 kcal mol(-1), with a quantum yield of more than 7%, This sy stem mimics the process by which photosynthetic bacteria convert light energy into ATP chemical potential.