Magnetically sensitive light-induced reactions in cryptochrome are consistent with its proposed role as a magnetoreceptor

Abstract

Among the biological phenomena that fall within the emerging field of “quantum biology” is the suggestion that magnetically sensitive chemical reactions are responsible for the magnetic compass of migratory birds. It has been proposed that transient radical pairs are formed by photo-induced electron transfer reactions in cryptochrome proteins and that their coherent spin dynamics are influenced by the geomagnetic field leading to changes in the quantum yield of the signaling state of the protein. Despite a variety of supporting evidence, it is still not clear whether cryptochromes have the properties required to respond to magnetic interactions orders of magnitude weaker than the thermal energy, k B T . Here we demonstrate that the kinetics and quantum yields of photo-induced flavin—tryptophan radical pairs in cryptochrome are indeed magnetically sensitive. The mechanistic origin of the magnetic field effect is clarified, its dependence on the strength of the magnetic field measured, and the rates of relevant spin-dependent, spin-independent, and spin-decoherence processes determined. We argue that cryptochrome is fit for purpose as a chemical magnetoreceptor.

Suppression of Arabidopsis flowering by near‐null magnetic field is mediated by auxin

“…Moreover, changes in transport of auxin and auxin signaling also affect Arabidopsis flowering [Sessions and Zambryski, 1995;Li et al, 2009]. Cryptochrome, a suggested magnetoreceptor, plays a major role in photoperiodic flowering in Arabidopsis [Guo et al, 1998;Mockler et al, 1999Mockler et al, , 2003Lin, 2000;Ritz et al, 2000;Gegear et al, 2008Gegear et al, , 2010Foley et al, 2011;Maeda et al, 2012]. Mutation of cryptochrome gene leads to delay of Arabidopsis flowering, while overexpression of cryptochrome gene promotes flowering [Guo et al, 1998;Yang et al, 2000].…”

Magnetic orientation of garden warblers ( Sylvia borin ) under 1.4 MHz radiofrequency magnetic field

“…Because, as known from quantum chemistry, covalent chemical bonds are formed by electrons with antiparallel magnetic moments (singlet spin state), the conversion of the pair of magnetic moments from antiparallel (singlet) to parallel (triplet) configuration and vice versa strongly affects the probability of recombination of the two radicals, and ultimately the yield of the entire photochemical reaction. The sensitivity of radical-pair reactions to magnetic fields is well known in chemistry [17]; recently, such a sensitivity was demonstrated in vitro for cryptochrome, the photosensitive protein that is considered as the candidate magnetoreceptor molecule of the bird compass [18]. However, the field intensities, required to considerably affect the photochemical process in the cryptochrome, were two orders of magnitude higher than that of the geomagnetic field.…”

The quantum needle of the avian magnetic compass

“…The primary sensory receptors are located in the eyes (2,3,(5)(6)(7), and directional information is processed bilaterally in a small part of the forebrain accessed via the thalamofugal visual pathway. The evidence currently points to a chemical sensing mechanism based on photo-induced radical pairs in cryptochrome flavoproteins in the retina (8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18). Anisotropic magnetic interactions within the radicals are thought to give rise to intracellular levels of a cryptochrome signaling state that depend on the orientation of the bird's head in the Earth's magnetic field (8,9,19).…”