8-Hydroxy-5-deazaflavin is a chromophore in some photolyases (photoreactivating enzymes). Photolyases are enzymes that use the energy of light to break covalent bonds between adjacent pyrimidines on a DNA strand. 8-Hydroxy-5-deazaflavin functions like the photochemical reaction center, translating light energy to facilitate the transfer of an electron to the pyrimidine dimer and breaking the pyrimidine-pyrimidine bonds by a free radical mechanism, as shown in Figure 25.10.