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Bionanodevice Beats Photosynthesis

Cofactors tethered to photosynthetic proteins achieves faster electron transfer than natural photosynthesis

by Celia Henry Arnaud
December 19, 2011 | A version of this story appeared in Volume 89, Issue 51

Credit: Proc. Natl. Acad. Sci. USA
This schematic depicts electron flow through a bionanoconstruct.
An illustration of a nanoconstruct with an electron donor (cytochrome c6, gray) and an electron acceptor (hydrogenase, lilac) are tethered directly to cyanobacterial photosystem I (PSI, green).
Credit: Proc. Natl. Acad. Sci. USA
This schematic depicts electron flow through a bionanoconstruct.

A hydrogen-producing nanodevice based on photosynthetic proteins has higher electron-transfer throughput than natural photosynthesis, scientists report (Proc. Natl. Acad. Sci. USA, DOI: 10.1073/pnas.1114660108). John H. Golbeck of Pennsylvania State University and coworkers tethered an electron donor and an electron acceptor directly to photosystem I (PSI) from cyanobacteria. They connected the electron donor cytochrome c6 (Cyt c6) via a zero-length diimide-based cross-linking agent and the electron acceptor—the [4Fe-4S] cluster of a cyanobacterial hydrogenase (H2ase)—via molecular wires containing three to 10 methylene groups or one or two phenyl groups. With a 1,8-octane­dithiol wire, the researchers achieved light-induced H2 evolution of 2,200 μmol H2 per mg chlorophyll per hour. The equivalent electron-transfer rate through the system was more than twice that of natural cyanobacterial photosynthesis. The nanodevice generated H2 for the four hours of each experiment, declining only when the sacrificial electron donor, sodium ascorbate, became depleted. The system retained its H2-evolving ability for 100 days at room temperature under anoxic conditions. Golbeck and coworkers suggest that tethering the proteins to the redox cofactors increases the electron-transfer rate by overcoming diffusion-based limitations.


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