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Spin chemistry in cryptochrome

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The five human senses are based on amazingly sensitive molecular processes: smell and taste are based on molecular recognition, hearing and touch on molecular mechanics, vision on molecular electronic excitation. Some animals have additional sensory capabilities; for example, some possess a magnetic sense used for orientation by means of the geomagnetic field. The magnetic sense has long been poorly understood since the underlying molecular process could not be identified, but recently some progress has been made. Surprisingly, animal vision has been implicated and evidence has been accumulated that animals can see the geomagnetic field. A long-hidden receptor in the eye, a protein aptly called cryptochrome, is likely involved. Unfortunately, cryptochrome exists only in minute amounts in animal eyes, e.g., those of migratory birds, so that only behavioral measurements on animals can be taken, but not physical measurements directly on cryptochromes. Fortunately, cryptochromes exist also in plants where they control hypocotyl growth inhibition in seedlings. Experimentalists have observed that cryptochrome-dependent responses in Arabidopsis thaliana seedlings are magnetic-field-dependent. Researchers have now also computationally demonstrated that light activation of plant cryptochrome is magnetic-field-dependent. A recent report showed that light excitation leads to cascading electron transfer in which electron spins are influenced by weak magnetic fields; the spin dynamics was found to influence the activation of cryptochrome. Arabidopsis thaliana cryptochrome can be produced in quantities large enough for physical measurements so that the door is now wide open for cracking the secret behind the long-mysterious magnetic sense of animals. More on our cryptochrome web site.