Studies of interaction between poly(allylamine hydrochloride) and double helix DNA by spectral methods

DNA interaction with cationic polyelectrolytes promises to be a versatile and effective synthetic transfection agent. This paper presents the study on interaction between a simple artificial cationic polymer, poly(allylamine hydrochloride) (PAA), and herring sperm DNA (hsDNA) using several spectroscopic methods, including light scattering, microscopic FTIR-, CD-spectroscopy and so on. The results show that PAA interacts with DNA through both the phosphate groups and the nitrogenous bases of DNA. The formation of DNA/PAA complex may change the micro-environment of double helix of DNA from B- to C-form and the great changes in DNA morphology occur when N:P ratio is near to 1.0. At the same time, the spectroscopic changes of ethidium bromide (EB) on its binding to DNA are utilized to study the interaction between PAA and DNA. Reversion of the maximum absorption wavelength (numax), reduction of induced circular dichroism and decrease in fluorescence intensity of DNA-EB on addition of PAA indicate that the formation of the complex between DNA and PAA is not in favor of the interaction between DNA and EB. The binding constant of EB and the number of binding sites per nucleotide decrease with increase in the concentrations of PAA, indicating noncompetitive inhibition of EB binding to DNA in the presence of PAA. It is also proved that the formation of the DNA/PAA complex is influenced by pH value and ionic strength.