Mechanism of benzo[a]pyrene diol epoxide induced deoxyribonucleic acid strand scission.
Mechanism of benzo[a]pyrene diol epoxide induced deoxyribonucleic acid strand scission.
复制标题
苯并[a]芘二醇环氧化物诱导脱氧核糖核酸链断裂的机制。
作者：
H. Gamper;J. Bartholomew;M. Calvin
约1%的（+/-）-7 β，8 α-二羟基-9 α，10 α-环氧-7，8，9，10-四氢苯并[a]芘（BaP-二醇环氧化物）DNA烷基化位点重排与链断裂在中性pH值。磷酸三酯水解和脱嘌呤/脱嘧啶链断裂作为这种现象的可能机制进行了严格检查。碱金属对切口的催化作用和反离子对切口的抑制作用均符合上述两种机理。切口的动力学，但是，是一个多步骤的反应，如脱嘌呤/脱嘧啶链断裂和检测的脱嘌呤位点的BaP-二醇环氧化物烷基化DNA的特征强烈支持这种机制。这些位点的数量，特别是在较低的反应水平，可能足以解释链断裂。没有直接证据表明通过磷酸三酯水解发生切口。对模型底物（包括磷酸三丁酯、DNA均聚物和TMV RNA）的研究表明，如果BaP-二醇环氧化物在DNA或RNA中形成磷酸三酯，则它们不会水解并发生链断裂。除了脱嘌呤/脱嘧啶位点，第二个碱敏感性重排产物存在于BaP-二醇环氧化物修饰的DNA。这些后者网站积累的时间和24小时后占4%的初始烷基化事件。虽然相对稳定的中性，他们自发地刻在高pH值的DNA骨架。这是可能的，这些网站代表了一个重排的主要N2鸟嘌呤加合物。
Approximately 1% of (+/-)-7 beta, 8 alpha-dihydroxy-9 alpha, 10 alpha-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene (BaP-diol epoxide) DNA alkylation sites rearrange with strand scission at neutral pH. Phosphotriester hydrolysis and depurination/depyrimidination strand scission were critically examined as possible mechanisms for this phenomenon. The catalysis of nicking by alkali and the inhibition of nicking by counterions were consistent with either mechanism. The kinetics of nicking, however, were characteristic of a multistep reaction such as depurination/depyrimidination strand scission and the detection of apurinic sites in BaP-diol epoxide alkylated DNA strongly supported this mechanism. The number of such sites, especially at lower reaction levels, was probably sufficient to account for strand scission. No direct evidence was obtained for nicking occurring through phosphotriester hydrolysis. Studies with model substrates, including dibutyl phosphate, DNA homopolymers, and TMV RNA, indicated that if BaP-diol epoxide forms phosphotriesters in DNA or RNA, they do not hydrolyze with strand scission. Besides apurinic/apyrimidinic sites, a second alkali-sensitive rearrangement product was present in BaP-diol epoxide modified DNA. These latter sites accumulated with time and after 24 h accounted for as much as 4% of the initial alkylation events. Although relatively stable at neutrality, they spontaneously nicked the DNA backbone at high pH. It is possible that these sites represent a rearrangement of the major N2 guanine adduct.