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Electron transfer in cryptochrome

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Animals and plants, together with other life forms, possess internal clocks that attune them to the daily rhythm on Earth. A sign of such clocks is jet lag, the discomfort experienced by humans when due to travel across several time zones our internal clocks need to be reset to the new time zone. Feed-back to local day light assists the resetting and a key light receptor serving the purpose is a protein called cryptochrome. The name was chosen as the receptor hid for a long time from the instruments of researchers, but today the name seems still appropriate as the physical mechanism of the receptor is shrouded in mystery and subject to dispute. Adding to the mystery is an apparent second role of cryptochrome, namely that of a sensor for the Earth' magnetic field, which helps migratory birds and many other animals in long-range navigation (see our magnetoreception page). The biological function of cryptochrome supposedly arises from a photoactivation reaction involving electron transfer, but the reaction pathway is difficult to resolve experimentally as the best available method, time-resolved spectroscopy, cannot identify unequivocally the photoproducts produced through cryptochrome light absorption. Experimentalists hate to admit the calamity, but likely the only way out are a combination of quantum-chemical and classical molecular dynamics calculations. Such calculations were recently performed and the results reported. The calculations demonstrate that after absorption an electron is transferred inside cryptochrome, the new state becomes stabilized through proton transfer and decays back to the protein's resting state on time scales allowing the protein, in principle, to act as a light as well as magnetic sensor. More details can be found on our cryptochrome webpage.