The article discusses the mechanism of radical transfer during the photoactivation of photolyase, a process crucial for DNA repair. The authors analyze the stability of tryptophan residues (W382, W359, and W306) in the protein, noting that their environments differ in polarity, which affects the energetics of electron transfer. They propose a mechanism where sequential electron transfers generate transient cation radicals, which are then deprotonated by water molecules. The study refutes a previous model that suggested a long-lived quartet state of FADH+ abstracting an electron from W306, as their experimental data show that the process occurs much faster. The authors conclude that charge compensation through simultaneous proton transfer is not necessary for intraprotein radical transfer. They also suggest that the conserved tryptophan residues are involved in the function of all photolyases and blue light receptors.The article discusses the mechanism of radical transfer during the photoactivation of photolyase, a process crucial for DNA repair. The authors analyze the stability of tryptophan residues (W382, W359, and W306) in the protein, noting that their environments differ in polarity, which affects the energetics of electron transfer. They propose a mechanism where sequential electron transfers generate transient cation radicals, which are then deprotonated by water molecules. The study refutes a previous model that suggested a long-lived quartet state of FADH+ abstracting an electron from W306, as their experimental data show that the process occurs much faster. The authors conclude that charge compensation through simultaneous proton transfer is not necessary for intraprotein radical transfer. They also suggest that the conserved tryptophan residues are involved in the function of all photolyases and blue light receptors.