Chain regularity and flow dichroism of deoxyribonucleic acids in solution

Abstract

AbstractDeoxyribonucleic acids (DNA's) extracted from several biological sources have been studied by means of the flow dichroism method, using the transparent coaxial cylinder apparatus. This study has two purposes: (1) to make clear the hydrodynamic behavior of the DNA chain, and the regularity in the orientation of purine and phrimidine bases about the molecular axis; and (2) to develop this particular flow dichroism method as an established device for the study of chain regularity of DNA and other chain polymers. The velocity gradient dependence of dichroism agrees well, to a first approximation, with the behavior of a model of a hydrodynamically equivalent ellipsoid in revolution. Differences between theoretical and empirical curves have been tentatively ascribed to the flexibility of the chain under consideration. Two kinds of data, 1 lie rotary diffusion coefficient and internal dichroism, have been evaluated by a graphical device in which the double logarithmic plots of reduced dichroism and velocity gradient of flow are compared with the theoretical curve. The data obtained have shown good reproducibility for DNA samples prepared by the same method from the same biological source. However, a remarkable difference in internal dichroism and rotary diffusion constant has been observed between DNA groups of different biological origin. The difference may be caused by fragmentation of DNA during the deproteinization procedure, bill the possibility that some of these differences originate in the biological source of the DNA cannot be denied. Orientation of purine and phrimidine bases in aqueous solution is found to be quite regular in direction, as predicted by the Watson–Crick model. Dichroic spectra have shown that the direction of the oscillator dipole corresponding to the 260 mμ absorption band has a different angular relationship to the helical axis than the oscillator dipole for the 220 mμ band.