Jorns M S, Baldwin E T, Sancar G B, Sancar A
J Biol Chem. 1987 Jan 5;262(1):486-91.
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.
DNA光解酶在需要可见光的反应中修复DNA中的嘧啶二聚体。来自大肠杆菌的光解酶通常作为一种蓝色蛋白质被分离出来，并且含有2种发色团：一个蓝色FAD自由基加上第二种发色团，当它在溶液中游离时在360nm处呈现最大吸收。FAD自由基的氧化伴随着活性的可逆丧失，这与酶黄素转化为FADox的比例成正比。将自由基定量还原为完全还原的FAD会使活性增加3倍。结果表明活性需要还原型黄素，并表明黄素可能在催化中作为电子供体。将蛋白质结合的第二种发色团计算出的吸收光谱（λmax = 390nm）与荧光数据以及二聚体修复的相对作用光谱进行比较，表明第二种发色团是光解酶中的荧光团，并且它确实在催化中作为敏化剂起作用。另一方面，含有减少量的第二种发色团的酶制剂并没有表现出相应较低的活性。这表明还原型黄素也可能在催化中作为敏化剂起作用。FAD自由基还原后酶的蓝色消失。完全还原的大肠杆菌酶表现出与酵母光解酶非常相似的吸收和荧光特性。这表明这两种酶可能含有相似的发色团，但就黄素的氧化还原状态而言是以不同形式被分离出来的。
