Measurement of DNA Counterion Condensation Due To Charge and Conformation Changes by Capillary Electrophoresis

• Main Authors: Ting-Rong, Lu, 呂定蓉
• Other Authors: Chunhung Wu
• Format: Others
• Language: zh-TW
• Published: 2001
• Online Access: http://ndltd.ncl.edu.tw/handle/70317825389247982237

碩士 === 淡江大學 === 化學學系 === 89 === DNA, a biopolymer bearing high negative charge, would be neutralized by electrostatic reaction with cationic counterions. In this study we measured DNA charge and conformation changes induced by the competing binding reactions of monovalent and multivalent counterions with DNA by using capillary electrophoresis techniques. The measured DNA mobility reduction after charge neutralization reaction could be used for the calculations of charge neutralization fraction and end-to-end distance change. The effects of cationic charge and concentration, ionic strength, DNA fragment size, and electroosmotic flow on the reductions of DNA electrophoretic mobilities were investigated. Three electrophoretic migration modes were observed for DNA fragments in the size range of 72 bp to 23.13kbp in this study. The measured charge neutralization fractions increased with increasing DNA fragment sizes and reached a plateau value (e.g., 0.873 for [Mg2+]=1000μΜ，0.25×TB, which was close to the DNA collapse point.) when the corresponding DNA fragments adopted the reptation with stretching model as the electrophoretic migration mechanism. We observed an increase in DNA charge neutralization fraction and a decrease in its end-to-end distance when increasing multivalent cation concentration or decreasing the ionic strength of the buffer. This observation was in agreement with the prediction of Manning’s counterion condensation theory. Under equivalent ionic strength, the charge neutralization abilities of various multivalent cations studied had the order of Spermine4+ > Co(NH3)63+ > Spermidine3+ > Mg2+ > Co2+ > Zn2+ > Cu2+. This order was the same as the result obtained for the calculation of end-to end distance change.