Epe B, Müller E, Adam W, Saha-Möller C R
Institute of Pharmacology and Toxicology, University of Würzburg, Germany.
Chem Biol Interact. 1992 Dec;85(2-3):265-81. doi: 10.1016/0009-2797(92)90067-u.
1,2-Dioxetanes are efficient sources of triplet excited carbonyl compounds, into which they decompose on thermal or photochemical activation. In the presence of DNA, the decomposition of dioxetanes gives rise to DNA modifications, which have been studied by means of specific repair endonucleases. Cyclobutane pyrimidine dimers, which are generated by triplet-triplet energy transfer, were detected by a UV endonuclease; they made up between 2% and 30% of the total modifications recognized by a crude repair endonuclease preparation from Micrococcus luteus. For various 1,2-dioxetanes, the yield of pyrimidine dimers was proportional to their triplet excitation flux. DNA strand breaks, sites of base loss (AP sites; recognized by exonuclease III and endonuclease IV) and dihydropyrimidines (recognized by endonuclease III) were found to represent only a small fraction of the modifications. The majority of the modifications detected were recognized by formamidopyrimidine-DNA glycosylase (FPG protein) and represent 8-hydroxyguanine (7,8-dihydro-8-oxoguanine) residues or other yet not defined base modifications which are recognized by this enzyme. The modifications were generated in similar relative yields by thermal and photo-induced decomposition of the 1,2-dioxetanes and therefore emanate under both conditions from the excited carbonyl compounds. The formation of the FPG protein-sensitive modifications was efficiently quenched by azide anions; the Stern-Volmer quenching of these modifications was 150-fold more effective than that of the pyrimidine dimers. The relative amounts of the two types of modifications were strongly dependent on the structure of the 1,2-dioxetanes and on the concentration of molecular oxygen. Singlet oxygen appears to be involved only to some extent in the generation of the FPG protein-sensitive base modifications as their yield was only moderately (approximately 2-fold) increased in D2O as solvent. A mechanism is suggested in which oxidized guanine is predominantly formed by a single-electron-transfer reaction of the triplet excited carbonyl product derived from the 1,2-dioxetane, followed by unknown secondary oxidations, which involve molecular oxygen and/or undecomposed 1,2-dioxetane.
1,2 - 二氧杂环丁烷是三线态激发羰基化合物的有效来源，它们在热或光化学活化作用下分解为三线态激发羰基化合物。在DNA存在的情况下，二氧杂环丁烷的分解会导致DNA修饰，人们借助特异性修复内切核酸酶对其进行了研究。通过紫外内切核酸酶检测到了由三线态 - 三线态能量转移产生的环丁烷嘧啶二聚体；它们在藤黄微球菌粗制修复内切核酸酶制剂识别的总修饰中占2%至30%。对于各种1,2 - 二氧杂环丁烷，嘧啶二聚体的产率与其三线态激发通量成正比。发现DNA链断裂、碱基缺失位点（AP位点；可被核酸外切酶III和内切核酸酶IV识别）和二氢嘧啶（可被内切核酸酶III识别）仅占修饰的一小部分。检测到的大多数修饰可被甲酰胺嘧啶 - DNA糖基化酶（FPG蛋白）识别，代表了8 - 羟基鸟嘌呤（7,8 -二氢 - 8 - 氧代鸟嘌呤）残基或该酶识别的其他尚未明确的碱基修饰。1,2 - 二氧杂环丁烷的热分解和光诱导分解产生的修饰相对产率相似 , 因此在这两种条件下均源自激发的羰基化合物。叠氮阴离子能有效淬灭FPG蛋白敏感修饰的形成；这些修饰的斯特恩 - 沃尔默淬灭效率比嘧啶二聚体高150倍。这两种修饰的相对量强烈依赖于1,2 - 二氧杂环丁烷的结构和分子氧浓度。单线态氧似乎仅在一定程度上参与了FPG蛋白敏感碱基修饰的产生，因为在以重水为溶剂时其产率仅适度增加（约2倍）。有人提出了一种机制，其中氧化鸟嘌呤主要由1,2 - 二氧杂环丁烷产生的三线态激发羰基产物的单电子转移反应形成，随后是未知的二次氧化反应，其中涉及分子氧和 / 或未分解的1,2 - 二氧杂环丁烷。
