Author Profile

Electron transfer reactions are at the heart of many biological processes. Whereas time-resolved electron paramagnetic resonance (EPR) is normally too slow to directly observe primary photochemical events, it has the unique capability of detecting the spin dynamics of radical pairs that often result from electron-transfer processes. In the last decade, such radical pairs have gained major interest as one possible mechanism by which migratory birds are able to sense the direction of Earth’s magnetic field for the purpose of navigation. The idea of a radical-pair based compass is quite old, but only recently candidate biomolecules, the cryptochromes, have been discovered. These proteins were proposed to form radical pairs upon illumination with blue light. Using time-resolved EPR together with point mutations of the respective proteins, we could demonstrate for the first time that cryptochromes indeed form such spin-correlated radical pairs. Furthermore, details of the spin–spin interaction in the radical pairs could be revealed from spectral simulations showing that cryptochromes are in principle well suited for being the compass molecule in, but not restricted to, migratory birds.