ИСТИНА

High density of negatively charged phosphate groups of the double helix provides the ability of DNA to form rather stable polyelectrolyte complexes (PECs) with polyamines. Complexes of DNA with synthetic oligo- and polycations were successfully used for increasing the efficiency of transformation of cells by the plasmides and for protection of DNA from splitting by cell nucleases. The prospects for addressing DNA packed in PEC species to the target cell has motivated an extension of studies of DNA-containing PECs in order to give precise control over their stability. The goal of the present work was to ascertain the influence of a structure of amine groups of polyamines on stability of DNA-containing PEC in water-salt solution at different pH. Polycations carrying primary, secondary, tertiary and quaternized amine groups in the chains were used. Particular emphasis has been placed on elucidation of a question how the polyamine is protonated in the presence of negatively charged DNA matrix of high charge density. Destruction of DNA-containing PECs caused by addition of low molecular weight electrolyte at different pH was studied by fluorescence quenching technique using the ability of cationic dye ethidium bromide to intercalate into free sites of DNA accompanied by ignition of ethidium fluorescence. Structure of amine groups of the polycations was shown to be a decisive factor of PECs stability. Thus, PECs formed by polycations with quaternary amine groups were pH-independent and the least tolerant to destruction by the addad salt. Primary amine groups of basic polypeptides provided the best stability of PECs in water-salt solutions under wide pH range. Moderate and pH-dependent stability was revealed for PECs included polyamines with tertiary amine groups in the chain or branchsd poly(ethylenimine) with primary, secondary and tertiary amine groups in the molecule. The data obtained appear to be the guideline in desigh of DNA-containing PECs with given and controllable stability. The design may be accomplished not only by proper choice of polyamine of one or another type, but by using of tailor-made polycations with given composition of amine groups of different structure in the chain as well. Thus, the destruction of PEC formed by DNA and random copolymer of 4-vinylpyridine and N-ethyl-4-vinylpyridinium bromide was pH-sensitive and could be performed under pH and ionic strength closed to the physiological conditions. This result appears to be particularly promising for addressing DNA packed in PEC species to the target cell.