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| - Analysis of the Role of Intraprotein Electron Transfer in Photoreactivation by DNAPhotolyase in Vivo
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| - Escherichia coli DNA photolyase contains FADH- as the catalytic cofactor. The cofactorbecomes oxidized to the FADH• blue neutral radical during purification. The E−FADH• form of theenzyme is catalytically inert but can be converted to the active E−FADH- form by a photoreductionreaction that involves intraprotein electron transfer from Trp306. It is thought that the E−FADH• form isalso transiently generated during pyrimidine dimer repair by photoinduced electron transfer, and it hasbeen suggested that the FADH• that is generated after each round of catalysis must be photoreducedbefore the enzyme can engage in subsequent rounds of repair. In this study, we introduced the Trp306Phemutation into the chromosomal gene and tested the non-photoreducible W306F mutant for photorepair invivo. We find that both wild-type and W306F mutant photolyases carry out at least 25 rounds of photorepairat the same rate. We conclude that photoreduction by intraprotein electron transfer is not part of thephotolyase photocycle under physiological conditions.
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