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Viability of superoxide-containing radical pairs as magnetoreceptors.

Research paper by Thomas C TC Player, P J PJ Hore

Indexed on: 26 Sep '21Published on: 16 Dec '19Published in: The Journal of chemical physics



Abstract

The ability of night-migratory songbirds to sense the direction of the Earth's magnetic field is increasingly attributed to a photochemical mechanism in which the magnetic field acts on transient radical pairs in cryptochrome flavoproteins located in the birds' eyes. The magnetically sensitive species is commonly assumed to be [FAD TrpH], formed by sequential light-induced intraprotein electron transfers from a chain of tryptophan residues to the flavin adenine dinucleotide chromophore. However, some evidence points to superoxide, O, as an alternative partner for the flavin radical. The absence of hyperfine interactions in O could lead to a more sensitive magnetic compass, but only if the electron spin relaxation of the O radical is much slower than normally expected for a small mobile radical with an orbitally degenerate electronic ground state. In this study we use spin dynamics simulations to model the sensitivity of a flavin-superoxide radical pair to the direction of a 50 μT magnetic field. By varying parameters that characterize the local environment and molecular dynamics of the radicals, we identify the highly restrictive conditions under which a O-containing radical pair could form the basis of a geomagnetic compass sensor. We conclude that the involvement of superoxide in compass magnetoreception must remain highly speculative until further experimental evidence is forthcoming.