title: Chemical amplification of magnetic field effects relevant to avian magnetoreception.
abstract: Magnetic fields as weak as the Earth's can change the yields of radical pair reactions even though the energies involved are orders of magnitude smaller than the thermal energy, kBT, at room temperature. Proposed as the source of the light-dependent magnetic compass in migratory birds, the radical pair mechanism is thought to operate in cryptochrome flavoproteins in the retina. Here we demonstrate that the primary magnetic field effect on flavin photoreactions can be amplified chemically by slow radical termination reactions under conditions of continuous photoexcitation. The nature and origin of the amplification are revealed by studies of the intermolecular flavin-tryptophan and flavin-ascorbic acid photocycles and the closely related intramolecular flavin-tryptophan radical pair in cryptochrome. Amplification factors of up to 5.6 were observed for magnetic fields weaker than 1 mT. Substantial chemical amplification could have a significant impact on the viability of a cryptochrome-based magnetic compass sensor.
authors.affiliation: Department of Chemistry, University of Oxford, Physical &Theoretical Chemistry Laboratory, Oxford OX1 3QZ, UK.
authors.forename: Daniel R
authors.initials: DR
authors.lastname: Kattnig
authors.affiliation: Department of Chemistry, University of Oxford, Inorganic Chemistry Laboratory, Oxford OX1 3QR, UK.
authors.forename: Emrys W
authors.initials: EW
authors.lastname: Evans
authors.affiliation: Department of Chemistry, University of Oxford, Inorganic Chemistry Laboratory, Oxford OX1 3QR, UK.
authors.forename: Victoire
authors.initials: V
authors.lastname: Déjean
authors.affiliation: Department of Chemistry, University of Oxford, Chemistry Research Laboratory, Oxford OX1 3TA, UK.
authors.forename: Charlotte A
authors.initials: CA
authors.lastname: Dodson
authors.affiliation: Department of Chemistry, University of Oxford, Chemistry Research Laboratory, Oxford OX1 3TA, UK.
authors.forename: Mark I
authors.initials: MI
authors.lastname: Wallace
authors.affiliation: Department of Chemistry, University of Oxford, Physical &Theoretical Chemistry Laboratory, Oxford OX1 3QZ, UK.
authors.forename: Stuart R
authors.initials: SR
authors.lastname: Mackenzie
authors.affiliation: Department of Chemistry, University of Oxford, Inorganic Chemistry Laboratory, Oxford OX1 3QR, UK.
authors.forename: Christiane R
authors.initials: CR
authors.lastname: Timmel
authors.affiliation: Department of Chemistry, University of Oxford, Physical &Theoretical Chemistry Laboratory, Oxford OX1 3QZ, UK.
authors.forename: P J
authors.initials: PJ
authors.lastname: Hore
mesh_terms: D000818:Animals; D001205:Ascorbic Acid / Q000737:chemistry; D056931:Cryptochromes / Q000737:chemistry*; D005415:Flavins / Q000737:chemistry; D008027:Light; D060526:Magnetic Fields; D009113:Muramidase / Q000737:chemistry; D011984:Sensory Receptor Cells / Q000502:physiology*; D014364:Tryptophan / Q000737:chemistry
chemical_list: D056931:Cryptochromes; D005415:Flavins; D014364:Tryptophan; D009113:Muramidase; D001205:Ascorbic Acid