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Direct measurement of picosecond charge separation in bacteriorhodopsin

Abstract

The Halobacterium halobium protein bacteriorhodopsin conservesthe energy of absorbed photons by converting it into a transmembrane proton gradient1. Light absorption bybacteriorhodopsin is thought to drive a photocycle of intermediate states linked to the pumping of protons across the plasma membrane. The earliest intermediate of this photocycle so far detected is formed in 11–15 ps2,3, and this step could involve a separation of charges within the protein2,4–9. Although an electrical response signal with a time course correlating with that of the photocycle has been measured for bacteriorhodopsin, so far it has not been possible to resolve a signal corresponding to the initial charge separation10–16. We report here the resolution by picosecond laser spectroscopy of an electrical signal apparently corresponding to a charge separation with a time constant of approximately 30 ps, which we attribute to the formation of the first intermediate of the bacteriorhodopsin photocycle.

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Groma, G., Szabó, G. & Váró, G. Direct measurement of picosecond charge separation in bacteriorhodopsin. Nature 308, 557–558 (1984). https://doi.org/10.1038/308557a0

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