Rates of spontaneous disintegration of DNA and the rate enhancements produced by DNA glycosylases and deaminases
Rates of spontaneous disintegration of DNA and the rate enhancements produced by DNA glycosylases and deaminases
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DOI：
10.1021/bi701480f
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发表时间：
2007-11-27
期刊：
影响因子：
2.9
通讯作者：
Wolfenden, Richard
中科院分区：
文献类型：
--
作者：
Schroeder, Gottfried K.;Wolfenden, Richard
为了估计 DNA 自发降解的替代途径的相对重要性以及催化这些反应的酶产生的速率增强，通过外推在中性磷酸盐缓冲液中 90 至 200 ℃ 温度范围内观察到的速率来确定 2'-脱氧核苷在 25 ℃ 下降解的速率常数和热力学活化参数。发现 2'-脱氧胞苷、1-甲基胞嘧啶和胞苷的脱氨率在实验误差范围内是相同的（t(1/2) 大约 20 年，37 摄氏度）。 2'-脱氧腺苷和2'-脱氧鸟苷的脱氨速率常数由于糖苷快速裂解而无法直接测定，通过假设甲基取代应产生合理的模型底物来估计。发现 9-甲基腺嘌呤和 9-甲基鸟嘌呤的脱氨基速率彼此相似（t(1/2) 大约 6000 年，37 摄氏度），并且比 2'-脱氧腺苷和 2'-脱氧鸟苷的糖苷裂解速率慢 10(2) 倍。 2'-脱氧腺苷、2'-脱氧鸟苷和2'-脱氧胞苷的脱氨基导致糖苷裂解速率加快。在 2'-脱氧胞苷的特殊情况下，脱氨基和糖苷水解在所有温度下都以非常相似的速率进行。糖苷裂解的半衰期范围从 2'-脱氧肌苷的 4 年到 2'-脱氧胞苷的 40 年（37 摄氏度）。通过与这些非催化反应的速率进行比较来估计，DNA 糖基化酶产生的速率增强明显小于。由脱氨酶和葡萄球菌核酸酶产生的那些。
To estimate the relative importance of alternate routes of spontaneous degradation of DNA and the rate enhancements produced by enzymes catalyzing these reactions, rate constants and thermodynamic activation parameters for the degradation of 2'-deoxynucleosides at 25 degrees C were determined by extrapolation of rates observed in the temperature range between 90 and 200 degrees C in neutral phosphate buffer. Rates of deamination of 2'-deoxycytidine, 1-methylcytosine, and cytidine were found to be identical within experimental error (t(1/2) approximate to 20 years, 37 degrees C). Rate constants for deamination of 2'-deoxyadenosine and 2'-deoxyguanosine, which could not be determined directly because of rapid glycoside cleavage, were estimated by assuming that methyl replacement should generate reasonable model substrates. The rates of deamination of 9-methyladenine and 9-methylguanine were found to be similar to each other (t(1/2) approximate to 6000 years, 37 degrees C) and similar to 10(2)-fold slower than the rates of glycoside cleavage in 2'-deoxyadenosine and 2'-deoxyguanosine. The deamination of 2'-deoxyadenosine, 2'-deoxyguanosine, and 2'-deoxycytidine led to accelerated rates of glycoside cleavage. In the exceptional case of 2'-deoxycytidine, deamination and glycoside hydrolysis proceed at very similar rates at all temperatures. Glycoside cleavage proceeds with half-times ranging from 4 years for 2'-deoxyinosine to 40 years for 2'-deoxycytidine (37 degrees C). The rate enhancements produced by DNA glycosylases, estimated by comparison with the rates of these uncatalyzed reactions, are found to be substantially smaller than. those produced by deaminases and staphylococcal nuclease.