Arizona State University College of Liberal Arts and Sciences

Using Light Energy to Generate Transmembrane Proton Gradients

Photosynthetic bacteria absorb light, transfer excitation energy to reaction centers, and use the excitation to move an electron across a biological membrane. The energy stored in the resulting transmembrane charge-separated state is used to pump protons across the membrane, generating a proton gradient, or proton motive force. The bacterium can then use this chemical energy to generate adenosine triphosphate, ATP, which can meet all its energy needs.

Our group has recently prepared a model system, shown diagrammatically below, which uses light energy to generate proton motive force. The heart of the system is a liposome vesicle comprised of a synthetic phospholipid bilayer. The bilayer is spanned by triad artificial reaction centers that undergo photoinduced electron transfer to generate a transmembrane charge-separated state. A shuttle quinone Qs uses this charge separation to transport protons across the membrane, establishing a proton gradient. The proton transport can be detected using a pH sensitive dye inside the liposome. ("Artificial Photosynthetic Reaction Centers in Liposomes: Photochemical Generation of Transmembrane Proton Potential," G. Steinberg-Yfrach, P. A. Liddell, S.-C. Hung, A. L. Moore, D. Gust and T. A. Moore, Nature (London), 385, 239-241 (1997)). Recently,we have incorporated a pmf-powered enzyme,ATP synthase from spinach chloroplast,into the liposomal bilayer. This enzyme uses the proton motive force provided by the light driven proton pumps to drive the synthesis of ATP from ADP and inorganic phosphate.("Light-Driven Production of ATP Catalysed by F0F1-ATP Synthase in an Artificial Photosynthetic Membrane,"G.Steinberg-Yfrach,J.-L. Rigaud, A.L.Moore, D.Gust and T.A.Moore, Nature, 392, 479 (1998).

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Photosynthesis Center

Arizona State University

Box 871604

Room PSD 209

Tempe, AZ 85287-1604


01 February 2006

phone: (480) 965-1963

fax: (480) 965-2747

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