KINETIC-ANALYSIS OF THE DEAMINATION REACTIONS OF CYCLOBUTANE DIMERS OF THYMIDYLYL-3',5'-2'-DEOXYCYTIDINE AND 2'-DEOXYCYTIDYLYL-3',5'-THYMIDINE
KINETIC-ANALYSIS OF THE DEAMINATION REACTIONS OF CYCLOBUTANE DIMERS OF THYMIDYLYL-3',5'-2'-DEOXYCYTIDINE AND 2'-DEOXYCYTIDYLYL-3',5'-THYMIDINE
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DOI：
10.1021/bi00061a009
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发表时间：
1993-03-16
期刊：
影响因子：
2.9
通讯作者：
RUZSICSKA, BP
中科院分区：
文献类型：
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作者：
LEMAIRE, DGE;RUZSICSKA, BP
用苯乙酮光敏化生成环丁烷二聚体dTpdC和dCpdT，并用反相高效液相色谱分离。每个二核苷一磷酸产生一个顺式、顺式异构体和两个反式、顺式异构体。选择dTpdC和dCpdT的顺式、顺式异构体和dTpdC的一种反式、顺式异构体(反式-反式糖苷异构体)研究了脱胺反应动力学。对pH依赖性的分析表明，脱氨是通过5，6-饱和胞嘧啶碱基的亚胺基团的水解和生成甲醇醇胺中间体来进行的。动力学参数的测定表明，对于这三种环丁烷二聚体，在生理pH下的速率控制步骤是氢离子对质子化的5，6-饱和胞嘧啶碱基的亲核攻击。动力学分析表明，顺式、顺式异构体的脱氨速度约为反式、顺式异构体的3倍，这是由于5，6-饱和胞嘧啶部分的pK(A)相差很大所致。胞嘧啶的亚胺基团和胸腺嘧啶的羰基之间的静电相互作用解释了顺式、顺式异构体相对于反式、顺式异构体的pK(A)的增加。提出了一种类似的相互作用来解释顺式、合式异构体和反式、合式异构体在甲醇胺中间体的分解方面的反应活性的相对差异。
The cyclobutane dimer photoproducts of dTpdC and dCpdT have been produced by acetophenone photosensitization and separated by reverse-phase HPLC. Each dinucleoside monophosphate was shown to produce one cis,syn isomer and two trans,syn isomers. Three of these photoproducts, namely, the cis,syn isomers of dTpdC and dCpdT and one trans,syn isomer (the syn-anti glycosidic isomer) of dTpdC were selected to study the deamination kinetics. Analysis of the pH dependence indicates that the deamination proceeds by the hydrolysis of the imido amide group of the 5,6-saturated cytosine base with the formation of a carbinolamine intermediate. Determination of the kinetic parameters showed that, for these three cyclobutane dimers, the rate-determining step at physiological pH is a nucleophilic attack of hydroxide ion on the protonated 5,6-saturated cytosine base. The kinetic analysis showed that the cis,syn isomers deaminate approximately 3 times faster than the trans,syn isomer, which is due to a large difference in pK(a) of the 5,6-saturated cytosine moiety. An electrostatic interaction between the iminium group of cytosine and the carbonyl group of thymine is proposed to account for the increase in pK(a) for the cis,syn isomers relative to the trans,syn isomer. A similar interaction is proposed to explain the relative difference in reactivity between the cis,syn isomers and the trans,syn isomer with regard to the breakdown of the carbinolamine intermediate.