A quantitative analysis of proflavine binding to polyadenylic acid, polyuridylic acid, and transfer RNA

Physico-chemical study of the complexes of "33258 Hoechst" with DNA and nucleohistone

The degree of binding of "33258 Hoechst" to DNA and nucleohistone has been determined by equilibrium dialysis and the properties of the complexes have been followed by different optical and electro-optical methods, after determining the orientation of the main transition moments within the dye molecule. The binding isotherm was found composed of a Langmuir-type and of a strongly cooperative component. The existence of two bound species yielded a continuous variation of most of the properties of the complexes studied as the amount of binding increased, while the hydrodynamic properties of the macromolecules were not affected. At low binding, the strongly bound dye molecules appeared to bind to highly fluorescent sites with their long axis oriented at 45 degree to the helix axis. As the binding proceeds, less fluorescent sites are cooperatively occupied and the inclination of these ligand molecules becomes closer to that of the base planes. These results are compatible with the formation of two external complexes with the double helical structure.

Molecular interactions and structure as analysed by fluorescence relaxation spectroscopy

Spectroscopic probes have become powerful tools in analysing the correlation between structure and function of biological macromolecules. Though these spectral methods cannot give as circumstantial information about the anatomy of a biological structure as, for example, X-ray diffraction they can provide information on physical properties at defined loci in a macromolecule which are not accessible by other techniques. Most important, spectroscopic studies have provided means to study the dynamics of structural changes and interactions in time domains spanning from nanoseconds and less up to infinite time.