Abstract: Alpha A. Lee†, Jason C. S. Lau, Hannah J. Hogben, Till Biskup‡, Daniel R. Kattnig and P. J. Hore⇑Department of Chemistry, Physical and Theoretical Chemistry Laboratory, University of Oxford, Oxford OX1 3QZ, UKe-mail: peter.hore{at}chem.ox.ac.uk↵† Present address: Mathematical Institute, University of Oxford, Oxford OX2 6GG, UK.↵‡ Present address: Institut für Physikalische Chemie, Albert-Ludwigs-Universität Freiburg, Freiburg, Germany.Abstract
There is growing evidence that the remarkable ability of animals, in particular birds, to sense the direction of the Earth's magnetic field relies on magnetically sensitive photochemical reactions of the protein cryptochrome. It is generally assumed that the magnetic field acts on the radical pair [FAD•− TrpH•+] formed by the transfer of an electron from a group of three tryptophan residues to the photo-excited flavin adenine dinucleotide cofactor within the protein. Here, we examine the suitability of an [FAD•− Z•] radical pair as a compass magnetoreceptor, where Z• is a radical in which the electron spin has no hyperfine interactions with magnetic nuclei, such as hydrogen and nitrogen. Quantum spin dynamics simulations of the reactivity of [FAD•− Z•] show that it is two orders of magnitude more sensitive to the direction of the geomagnetic field than is [FAD•− TrpH•+] under the same conditions (50 µT magnetic field, 1 µs radical lifetime). The favourable magnetic properties of [FAD•− Z•] arise from the asymmetric distribution of hyperfine interactions among the two radicals and the near-optimal magnetic properties of the flavin radical. We close by discussing the identity of Z• and possible routes for its formation as part of a spin-correlated radical pair with an FAD radical in cryptochrome.
animal navigationflavinmagnetic compassradical pair mechanismspin dynamicsReceived November 15, 2013.Accepted March 3, 2014.© 2014 The Author(s) Published by the Royal Society. All rights reserved.