[Compaction of 2-chain DNA as a method of procedure in determining its binding constant with antibiotics].

The binding of antibiotics and dyes with a compact form of DNA produced in water-salt solutions containing polyethylenglycol (PEG) presents a possibility of studying antibiotic interaction with DNA molecules contained in biological objects, such as viruses and chromosomes, since the compact form of DNA reflects some DNA properties in vivo. Possibly the use of the compact and not the "open" or linear form of DNA in chemical reactions will provide data on the efficiency of the compound "action" under conditions close to intracellular ones. The results well be useful in screening substances with "optimal" pharmacological effect. The paper presents a method for determination of the constant of antibiotic or dye binding with DNA and two-chain synthetic polynucleotides in water-salt solutions containing PEG. The method is based on "elimination" of the DNA molecules in the form of compact particles bound in a complex with an antibiotic or a dye. Comparison of the data with the results of estimation of the constants of antibiotic binding with DNA by the routine methods showed close conformity of the binding constants determined by different methods. It was found that the value of the binding constant of the antibiotics studied slightly depended on the structural state of DNA. The value was practically the same for the linear and the compact forms of DNA.