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Updated: Feb 9, 2026

Characterization of Biological Absorption Spectra Spanning the Visible to the Short-Wave Infrared
Published on: January 10, 2025
Absorption Spectra of FAD Embedded in Cryptochromes
Claus Nielsen1, Morten S Nørby1, Jacob Kongsted1
1Department of Physics, Chemistry and Pharmacy , University of Southern Denmark , DK-5230 Odense M , Denmark.
Abstract:
The magnetic compass sense utilized by migratory birds for long-distance navigation functions only once light of a certain wavelength is present. This piece of evidence fits partially with the popular hypothesis of chemical magnetoreception in cryptochrome proteins, located in the bird retina. According to this hypothesis a magnetosensitive radical pair is produced after photoexcitation of an FAD cofactor inside cryptochrome, and as such the absorption properties of FAD are of crucial importance for cryptochrome activation. However, we reveal that absorption spectra of FAD show very little variation between six different cryptochromes, suggesting that the electronic transitions are barely affected by the chemical differences in the proteins. This conclusion hints on the presence of a secondary photoreceptor or cofactor that could be necessary to explain green-light-activated magnetoreception in birds.
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