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Bioelectromagnetism

FIGURE 5.13 A tentative reaction scheme of an RP-based magnetic compass involving dark-state reoxidation of

•

the fully reduced FADH⁻, the superoxide radical anion (O2

− )n and radical scavenging to avoid the detriment of fast

spin relaxation associated with the latter. Details are discussed in the main text. (Adapted from Kattnig (2017).)

Recently, a tentative scheme has been proposed to show the dark-state reoxidation of the fully reduced

FADH⁻, the superoxide radical anion (O^•

2

− ) and radical scavenging to avoid the detriment of fast spin

relaxation associated with the latter. Te spin-correlated FADH^• / O^•

2

− -RP is formed in a dark-state reac­

tion from the fully reduced favin, FADH⁻, and molecular oxygen. Due to the ³Σ ground state of O2, this

RP is generated exclusively in a (local) triplet state, which corresponds to both doublet and quartet states

in the combined system including the initially uncorrelated radical scavenger. Te doublet and quartet

states interconvert via hyperfne interactions in FADH^• and C^• and the Zeeman interactions of all radi­

cals. Te MFE arises from the competition between the regeneration of the fully oxidized FAD and the

spin-independent formation of the signaling state. It is assumed that the singlet recombination of the

FADH^• / O^•

2

− -RP produces hydrogen peroxide (H2O2), possibly via the C4a-hydroperoxy-favin, and that

C^• reoxidizes FADH^• to FAD (Massey, 1994). Both assumptions are not critical as long as the products

of these spin-selective reactions are disparate from the signaling state. Note that the favin/tryptophan

RP intermediate produced in the light-activation step is likely to be magnetosensitive as well. It is also

assumed that the scavenger radical C^• is produced in the course of the photoreduction. It could be an

oxidized electroactive residue within the protein (Kattnig, 2017) (Figure 5.13).

5.5 Magnetic Fields with a Higher Intensity

with Respect to Geomagnetic Field

MFE depends on the strength of the MF, which can be classifed as weak (<1 mT), moderate (1 mT to 1 T),

strong (1–5 T), and ultrastrong (>5 T). Weak MF, as the GMF, can be perceived by animals and plants as

described above. Strong and ultrastrong felds are of sufcient intensity to alter the preferred orientation

of a variety of diamagnetic anisotropic organic molecules and their efects have been attributed to this

mechanism. Moderate intensity static MFs (SMFs) infuence those biological systems where function

depends on the properties of excitable membranes. Inasmuch as these felds are insufcient to infuence

individual molecules, there must be something unique about biological membranes that make them

susceptible to these felds in a way that would alter cell function (Rosen, 2003).