Electron–Electron Dipolar Interaction Poses a Challenge to the Radical Pair Mechanism of Magnetoreception

Abstract

A visual magnetic sense in migratory birds has been hypothesized to rely on a radical pair reaction in the protein cryptochrome. In this model, magnetic sensitivity originates from coherent spin dynamics, as the radicals couple to magnetic nuclei via hyperfine interactions. Prior studies have often neglected the electron−electron dipolar (EED) coupling from this hypothesis. We show that EED interactions suppress the anisotropic response to the geomagnetic field by the radical pair mechanism in cryptochrome and that this attenuation is unlikely to be mitigated by mutual cancellation of the EED and electronic exchange coupling, as previously suggested. We then demonstrate that this limitation may be overcome by extending the conventional model to include a third, nonreacting radical. We predict that hyperfine effects could work in concert with three-radical dipolar interactions to tailor a superior magnetic response, thereby providing a new principle for magnetosensitivity with applications for sensing, navigation, and the assessment of biological magnetic field effects.

Effect of Intermittent ELF MF on Umbilical Cord Blood Lymphocytes

“…Since the present study was not designed to unravel the mechanisms underlying the observed effects, our results pose little preference for any of the interaction models proposed in the literature [Binhi, 2002; Hore and Mouritsen, 2016; Babcock and Kattnig, 2020]. In spite of this, our results do suggest the presence of an amplitude window, so they are prone to be explained by models that predict ranges of enhanced effectiveness.…”

The Magnetic Compass of Birds: The Role of Cryptochrome

“…FADH- is then re-oxidized independently of light to FADox. During this step, a second radical pair is formed ( Figure 2 ), possibly with O 2 ∙ (see, e.g., Ritz et al, 2009 ; Müller and Ahmad, 2011 ), but the true partner of FADH ∙ and details of this process are still under debate (see, e.g., Hogben et al, 2009 ; Lee et al, 2014 ; Worster et al, 2016 ; Kattnig, 2017 ; Nielsen et al, 2017 ; Player and Hore, 2019 ; Babcock and Kattnig, 2020 ; Procopio and Ritz, 2020 ).…”

Cryptochromes: Photochemical and structural insight into magnetoreception

“…63,116 We note that several have been recently proposed, including a light-driven mechanism mirroring photolyase chemistry, and alternative radical pair components through protein-protein or small molecule interactions, 4,14,51 potentially including a third radical. 117 The recent advent of a tractable genetic model in the monarch butterfly should greatly expand our understanding of magenetoreception over the next several years.…”