Figure 3.

Cryptochrome activation and inactivation reactions. Blue light activates cryptochrome through absorbing a photon by the flavin cofactor. FAD becomes promoted to an excited FAD^* state and receives an electron from a nearby tryptophan, leading to the formation of the [FADH• + Trp•] radical pair, which exists in singlet ⁽¹⁾ and triplet ⁽³⁾ overall electron spin states by coherent geomagnetic field-dependent interconversions. Under aerobic conditions, FADH• slowly reverts back to the initial inactive FAD state through the also inactive FADH⁻ state of the flavin cofactor (Modified from Occhipinti et al., 2014).