AbstractsBiology & Animal Science

A fluorescent dye, 1-dimethylaminonaphthalene-5-sulfonyl chloride (dansyl chloride), was covalently bonded to polylysine. The dansyl tagged polylysine was complexed to DNA by gradient dialysis. The polarization and intensity of fluorescence of the dansyl and the turbidity of the complex were measured as a function of salt concentration for a variety of salts. By assuming a two state model for the system, namely complexed and uncomplexed polylysine, the fraction, f, of the dansyl polylysine complexed to the DNA was determined from the polarization and intensity of fluorescence data. Under the more stringent assumption that the fluorescent intensity of the dansyl polylysine molecule was dependent only on whether or not it was bound to the DNA, f was calculated from the intensity of fluorescence data alone. The results were in good agreement with the results of the polarization measurements. The fractional change in the turbidity of the solution of the DNA-polylysine complex was also found to be reasonably close to the value of f as determined by polarization. This indicates that the scattering unit is a well defined system. The effectiveness of the ions in dissociating the complex is in the order SCN⁻, ClO₄⁻>NO₃⁻> Br ⁻>Cl⁻>C₂H₃O₂⁻ and Mg⁺⁺>Li⁺>NH₄⁺, Na⁺>K⁺. The dissociation curve of a complex of polylysine with A-T rich salmon sperm DNA appears to be nearly identical to that of the G-C rich Micrococcus lysodeikticus DNA-polylysine complex. The pH titration of the complex showed that the association of polylysine with the DNA stabilized the polylysine against the loss of its protons. NaCI is more effective in dissociating the DNA-polylysine complex in an aqueous solution than it is when the complex is in a 50 volume percent methanol solution.