ИСТИНА

Cryptochrome proteins are thought to function as magnetoreceptors supporting navigation of migratory birds. The radical-pair hypothesis suggests that the avian cryptochrome hosts photochemically generated radical pairs which undergo either spin recombination or formation of the photoproduct with yields depending on the orientation of the cryptochrome in the geomagnetic field. Recent studies (H.G. Hiscock et al, PNAS 2016 113 4634) demonstrated the existence of a sharp feature in the output of the cryptochrome-based magnetic sensor which arises from the avoided crossing of the spin-energy levels of the radical pair. Here we concentrate on the individual flavin and tryptophane radicals from the Drosophila Melanogaster cryptochrome protein, and find that each radical displays the avoided crossing of the energy levels corresponding to the particular electron spin states in a weak magnetic field. This behavior arises from axial symmetry of the hyper-fine electron-nucleus spin interaction defined by the -electronic character of the radical. The level crossing corresponds to the orientation of the symmetry axis orthogonal to the weak magnetic field, and the electron spin projections on the symmetry axis take the values +1/2 and 1/2, sharply interchanging at the crossing. The spin flip in the individual radicals would contribute to altering the singlet and triplet population of the radical pair, providing thereby the sharp direction sensitivity of the magnetoreceptor.