Heelis P F, Sancar A
Biochemistry. 1986 Dec 16;25(25):8163-6. doi: 10.1021/bi00373a006.
Escherichia coli DNA photolyase contains a stable flavin neutral blue radical that is involved in photosensitized repair of pyrimidine dimers in DNA. We have investigated the effect of illumination on the radical using light of lambda greater than 520 nm from either a camera flash or laser. We find that both types of irradiations result in the photoreduction of the flavin radical with a quantum yield of 0.10 +/- 0.02. While photoreduction with the camera flash is minimal in the absence of an electron donor (dithiothreitol), laser flash photolysis at 532 nm reduces the flavin to the same extent in the presence or absence or an electron donor. Thus, it is concluded that the primary step in photoreduction involves an electron donor that is a constituent of the enzyme itself. Laser flash photolysis produces a transient absorption band at 420 nm that probably represents the absorption of the lowest excited doublet state (2(1)IIII*) of the radical and decays with first-order kinetics with k1 = 0.8 X 10(6) s-1. The photoreduction data combined with the results of recent studies on the activity of dithionite-reduced enzyme suggest that electron donation by excited states of E-FADH2 is the mechanism of flavin photosensitized dimer repair by E. coli DNA photolyase.
大肠杆菌DNA光解酶含有一种稳定的黄素中性蓝自由基，它参与DNA中嘧啶二聚体的光致敏修复。我们使用相机闪光灯或激光发出的波长大于520nm的光研究了光照对该自由基的影响。我们发现，这两种类型的照射都会导致黄素自由基的光还原，量子产率为0.10±0.02。在没有电子供体（二硫苏糖醇）的情况下，相机闪光灯的光还原作用很小，而在532nm处的激光闪光光解在有无电子供体的情况下将黄素还原到相同程度。因此，可以得出结论，光还原的第一步涉及作为酶自身组成部分的电子供体。激光闪光光解在420nm处产生一个瞬态吸收带，这可能代表自由基最低激发双重态（2(1)IIII*）的吸收，并以一级动力学衰减，k1 = 0.8×10(6) s-1。光还原数据与最近关于连二亚硫酸盐还原酶活性的研究结果相结合，表明E-FADH2激发态的电子供体是大肠杆菌DNA光解酶进行黄素光致敏二聚体修复的机制。
