DNA的剪切降解
Shear degradation of DNA.
作者信息
Adam R E, Zimm B H
出版信息
Nucleic Acids Res. 1977;4(5):1513-37. doi: 10.1093/nar/4.5.1513.
A concentric-cylinder flow-birefringence instrument is used to generate sufficient shear fields to break T2 DNA (M = 1.2 X 10(8)) and E. coli DNA (M = 2.5 X 10(9)) in dilute solution. Breakage is monitored in situ by measuring the change in birefringence relaxation after the flow has been stopped. The breakage of T2 DNA follows first-order kinetics. Rate constants are obtained as functions of shear rate and viscosity (varied by adding glycerol). The data are fitted by a modified Arrhenius equation, assuming that stess increases the rate by lowering the activation energy. The rate increases with temperature, pH, and water concentration, and appears to be a base-catalyzed hydrolysis of the phosphate-ester linkage. La3+ ions catalyze the reaction. E. coli DNA was reduced to half molecules at a shear stress of 0.4 dynes/cm2, which is about 2500 times less than that required for T2. The difference in rates is accounted for in part by the difference in size of the two, but may also reflect the presence of many single-strand nicks in the coli DNA.
一种同心圆柱流动双折射仪器用于在稀溶液中产生足够的剪切场，以断裂T2 DNA（分子量为1.2×10⁸）和大肠杆菌DNA（分子量为2.5×10⁹）。通过在流动停止后测量双折射弛豫的变化来原位监测断裂情况。T2 DNA的断裂遵循一级动力学。速率常数作为剪切速率和粘度（通过添加甘油来改变）的函数获得。假设应力通过降低活化能来提高速率，数据用修正的阿伦尼乌斯方程拟合。速率随温度、pH值和水浓度增加，并且似乎是磷酸酯键的碱催化水解。La³⁺离子催化该反应。在0.4达因/平方厘米的剪切应力下，大肠杆菌DNA被还原为半分子，这比T2所需的剪切应力小约2500倍。速率差异部分归因于两者大小的差异，但也可能反映了大肠杆菌DNA中存在许多单链切口。
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