Chemical amplification of magnetic field effects relevant to avian magnetoreception


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.

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Figure 1: Intermolecular radical pair reactions of flavins.
Figure 2: Amplified MFEs in intermolecular reactions of flavins.
Figure 3: Characteristics of the amplified MFE.
Figure 4: Amplified MFEs in the low-field region.
Figure 5: Intramolecular radical pair reactions of cryptochromes.
Figure 6: Amplified MFEs in a cryptochrome.
Figure 7: Simulations of changes in radical concentrations induced by a magnetic field.


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We thank N. Baker for expert technical assistance. E.W.E. is indebted to the Engineering and Physical Sciences Research Council and SABMiller plc for his doctoral scholarship. C.A.D. gratefully acknowledges her current Imperial College Junior Research Fellowship. We are grateful to the following for financial support: the Defense Advanced Research Projects Agency (QuBE: N66001-10-1-4061), the European Research Council (under the European Union's 7th Framework Programme, FP7/2007-2013/ERC grant agreement No. 340451), the Air Force Office of Scientific Research (Air Force Materiel Command, USAF award No. FA9550-14-1-0095) and the EMF Biological Research Trust.

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D.R.K. and E.W.E. contributed equally to this work. D.R.K., E.W.E. and V.D. designed and performed the experiments. D.R.K. and E.W.E. analysed the data. C.A.D. advised on the production of the AtCry1 samples. M.I.W. helped oversee the fluorescence microscopy experiments. C.R.T., S.R.M. and P.J.H. coordinated the study. P.J.H., D.R.K. and E.W.E. wrote the paper. All the authors discussed the results and commented on the manuscript.

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Correspondence to P. J. Hore.

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Kattnig, D., Evans, E., Déjean, V. et al. Chemical amplification of magnetic field effects relevant to avian magnetoreception. Nature Chem 8, 384–391 (2016).

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