[Effect of organic solvents on DNA conformation by fluorescent probe method]

In this paper, the conformation of calf thymus DNA(DNA) is investigated in some common solvents by spectrofluorimetry. The result of fluorescence spectra and scatchard plot indicate that the binding constant between DNA and ethidium bromide (EB) will decrease with the increasing concentration of ethanol, and the number of binding sites will increase. The change of binding constant elucidate that the interaction between DNA and EB will become poor, and the change of binding sites shows that the conformation of DNA has transformed from B-form to A-form. In the course of this change, the distance between both neighboring base plan will be decreased. When the EB molecule just fit into the interval, the fluorescence intensity will be maximum. When DNA shrink further, the EB molecules will be excluded from DNA, then the fluorescence intensity will decrease. Although the conformation of DNA will be changed in organic solvents, it will not denaturate or dehelix, because the absorption of DNA will not increase greatly with the increasing concentration of ethanol. The melting temperature of DNA decreases continually as the weight fraction of ethanol concentration is increased. It shows that the DNA will be more distabilized in ethanol, so it helps to explain some phenomena of life and physiology. Meanwhile, the results offer an opportunity to further study the interaction DNA and insoluble drugs.