Abstract
DNA photolyase repairs pyrimidine dimers in DNA in a reaction that requires visible light. Photolyase from Escherichia coli is normally isolated as a blue protein and contains 2 chromophores: a blue FAD radical plus a second chromophore that exhibits an absorption maximum at 360 nm when free in solution. Oxidation of the FAD radical is accompanied by a reversible loss of activity which is proportional to the fraction of the enzyme flavin converted to FADox. Quantitative reduction of the radical to fully reduced FAD causes a 3-fold increase in activity. The results show that a reduced flavin is required for activity and suggest that flavin may act as an electron donor in catalysis. Comparison of the absorption spectrum calculated for the protein-bound second chromophore (lambda max = 390 nm) with fluorescence data and with the relative action spectrum for dimer repair indicates that the second chromophore is the fluorophore in photolyase and that it does act as a sensitizer in catalysis. On the other hand, enzyme preparations containing diminished amounts of the second chromophore do not exhibit correspondingly lower activity. This suggests that reduced flavin may also act as a sensitizer in catalysis. The blue color of the enzyme is lost upon reduction of the FAD radical. The fully reduced E. coli enzyme exhibits absorption and fluorescence properties very similar to yeast photolyase. This indicates that the two enzymes probably contain similar chromophores but are isolated in different forms with respect to the redox state of the flavin.
Highlights
DNA photolyase repairs pyrimidine dimers inDNA can promote cleavage in the presence of certain photosensiin areaction that requires visible light
Photolyase tizing agents (Helene and Charlier, 1971,1977; Rothand from Escherichia coli is normally isolated as a blue Lamola, 1972). These model studies suggested that the phoprotein and contains2 chromophores: a blue FAD rad- tolyase reaction might be a photosensitized process involving ical plus a second chromophore that exhibits an ab- an enzyme-bound chromophore that absorbs visible light. sorption maximum at 360 nm when free in solution
While the fluorescence emission relative action spectrum dfiomrer repair indicates that (Jorns, et al, 1984; Sancar and Sancar, 1984) of the enzyme the second chromophore is the fluorophore in pho- at 470-480 nm is not due to the flavin radical, identification tolyase and thatit does act as a sensitizer in catalysis. of the fluorophore remained tentative since the absorption
Summary
Photolyase tizing agents (Helene and Charlier, 1971,1977; Rothand from Escherichia coli is normally isolated as a blue Lamola, 1972) These model studies suggested that the phoprotein and contains chromophores: a blue FAD rad- tolyase reaction might be a photosensitized process involving ical plus a second chromophore that exhibits an ab- an enzyme-bound chromophore that absorbs visible light. Exposure of DNA to ultraviolet light results in the formation of cyclobutane dimers between adjacent pyrimidine resstrongly suggest that the E. coli and yeast enzymes have a very similar chromophore composition despite apparent difidues These dimers can be repaired byDNA photolyase, a ferences in the absorption spectra of the isolated enzymes.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
