Creatures as varied as mammals, fishes, insects, reptiles, and birds have an intriguing 'sixth' sense that allows
them to navigate in the Earth's magnetic field. Despite decades of study, the physical basis of this sense remains
elusive. A likely mechanism is furnished by magnetic field sensitive reactions occurring in the retina of animal eyes.
A decade ago it was suggested (see our magnetoreception page
that the photoreceptor cryptochrome, arising in the retina, endows birds with magnetoreceptive abilities. The
hypothesis gained support during the last years, after it had been shown that the protein exhibits properties
required for an animal magnetoreceptor to operate properly.
(see prior highlights on
A Compass in the Eye, July 2010
Where's North, Ask Superoxide, July 2009
Animal Magnetic Sense Shared by Plant, April 2007
However, the biophysical mechanism of cryptochrome
activation and signaling is still poorly understood.
A recent study
proposed a theoretical analysis method for
identifying cryptochrome's signaling reactions involving comparison of measured and calculated reaction kinetics.
Application of the method suggest a light-driven reaction cycle which combines electronic excitation with
electron and proton transfer reactions in the protein. More details on cryptochrome functioning as a
light-driven magnetic compass can be found on our