BINDING OF SMALL CATIONS TO DEOXYRIBONUCLEIC ACID . NUCLEOTIDE SPECIFICITY

The relative affinities of a number of small weakly bound cations for deoxyribonucleic acids of varying base composition have been measured. Dialysis equilibrium measurements were carried out by allowing two deoxyribonucleic acids of different base compositions to compete with each other for a strongly bound “test” cation, such as Ca2+ or spermine, in the presence of excess concentrations of the weakly bound cation under investigation. The binding properties of the weakly bound cation were deduced from its effect upon the distribution of strongly bound cation. The method does not involve a complicated theoretical analysis of binding data, and the use of direct competition experiments reduces the error in the computation of relative binding affinities. We find that Na+, Li+, Cs+, and K+, as well as arginine, lysine, and tetralysine, are bound equally tightly to deoxyribonucleic acids of any base composition. Tetramethyl- and tetraethylammonium ions, as well as some other small teiraalkylammonium ions, are bound more tightly to adenine-thymine-rich deoxyribonucleic acids than to guanine-cytosine-rich deoxyribonucleic acids. © 1969, American Chemical Society. All rights reserved.