Evidence for concerted electron proton transfer in charge recombination between FADH- and 306Trp• in Escherichia coli photolyase.

Proton-coupled electron-transfer (PCET) is a mechanism of great importance in protein electron transfer and enzyme catalysis, and the involvement of aromatic amino acids in this process is of much interest. The DNA repair enzyme photolyase provides a natural system that allows for the study of PCET using a neutral radical tryptophan (Trp(•)). In Escherichia coli photolyase, photoreduction of the flavin adenine dinucleotide (FAD) cofactor in its neutral radical semiquinone form (FADH(•)) results in the formation of FADH(-) and (306)Trp(•).