TY - JOUR
T1 - Active transport of Ca2+ by an artificial photosynthetic membrane
AU - Bennett, Ira
AU - Vanegas Farfano, Hebe M.
AU - Bogani, Federica
AU - Primak, Alex
AU - Liddell, Paul A.
AU - Otero, Luis
AU - Sereno, Leonides
AU - Silber, Juana J.
AU - Moore, Ana
AU - Moore, Thomas
AU - Gust, Devens
N1 - Funding Information:
Acknowledgements This work is supported in part by the US Defense Advanced Research Program Agency (DARPA) through the Army Research Office (ARO). H. Z. and J. L. thank DARPA for support through Louisiana Tech University.
Funding Information:
Acknowledgements This research was supported by the US Department of Energy and the Harrington Arthritis Research Center.
PY - 2002/11/28
Y1 - 2002/11/28
N2 - Transport of calcium ions across membranes and against a thermodynamic gradient is essential to many biological processes, including muscle contraction, the citric acid cycle, glycogen metabolism, release of neurotransmitters, vision, biological signal transduction and immune response. Synthetic systems that transport metal ions across lipid or liquid membranes are well known, and in some cases light has been used to facilitate transport. Typically, a carrier molecule located in a symmetric membrane binds the ion from aqueous solution on one side and releases it on the other. The thermodynamic driving force is provided by an ion concentration difference between the two aqueous solutions, coupling to such a gradient in an auxiliary species, or photomodulation of the carrier by an asymmetric photon flux. Here we report a different approach, in which active transport is driven not by concentration gradients, but by light-induced electron transfer in a photoactive molecule that is asymmetrically disposed across a lipid bilayer. The system comprises a synthetic, light-driven transmembrane Ca2+ pump based on a redox-sensitive, lipophilic Ca2+-binding shuttle molecule whose function is powered by an intramembrane artificial photosynthetic reaction centre. The resulting structure transports calcium ions across the bilayer of a liposome to develop both a calcium ion concentration gradient and a membrane potential, expanding Mitchell's concept of a redox loop mechanism for protons to include divalent cations. Although the quantum yield is relatively low (∼1 per cent), the Ca2+ electrochemical potential developed is significant.
AB - Transport of calcium ions across membranes and against a thermodynamic gradient is essential to many biological processes, including muscle contraction, the citric acid cycle, glycogen metabolism, release of neurotransmitters, vision, biological signal transduction and immune response. Synthetic systems that transport metal ions across lipid or liquid membranes are well known, and in some cases light has been used to facilitate transport. Typically, a carrier molecule located in a symmetric membrane binds the ion from aqueous solution on one side and releases it on the other. The thermodynamic driving force is provided by an ion concentration difference between the two aqueous solutions, coupling to such a gradient in an auxiliary species, or photomodulation of the carrier by an asymmetric photon flux. Here we report a different approach, in which active transport is driven not by concentration gradients, but by light-induced electron transfer in a photoactive molecule that is asymmetrically disposed across a lipid bilayer. The system comprises a synthetic, light-driven transmembrane Ca2+ pump based on a redox-sensitive, lipophilic Ca2+-binding shuttle molecule whose function is powered by an intramembrane artificial photosynthetic reaction centre. The resulting structure transports calcium ions across the bilayer of a liposome to develop both a calcium ion concentration gradient and a membrane potential, expanding Mitchell's concept of a redox loop mechanism for protons to include divalent cations. Although the quantum yield is relatively low (∼1 per cent), the Ca2+ electrochemical potential developed is significant.
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U2 - 10.1038/nature01209
DO - 10.1038/nature01209
M3 - Article
C2 - 12459780
AN - SCOPUS:18744403095
SN - 0028-0836
VL - 420
SP - 398
EP - 401
JO - Nature
JF - Nature
IS - 6914
ER -