ON INTERACTION OF NUCLEOTIDES WITH BASIC POLYAMINO ACIDS . COOPERATIVE BINDING BEHAVIOR

The binding of nucleoside monophosphates by poly‐l‐arginine and guanosine monophosphate by poly‐l‐lysine at low ionic strength and pH 7 consists of two phases. At low values of τ (number of bound nucleotides per amino acid residue) the binding behavior can be fitted to the Langmuir isotherm; at high τ values the binding behavior can be fitted to the Langmuir isotherm; at high τ values the binding is cooperative and accompanied by precipitation of a polyamino acid–nucleotide complex. Three different mathematical approaches were used to describe the binding behavior of the cooperative phase. The results indicate that the magnitude of the parameters for nearest neighbor interaction of bound nucleotides parallels the tendency of self‐association of the respective bases. A value of about 2 kcal/mole was determined for the nearest beighbor interaction energy of guanosine 5′ ‐phosphate with poly‐l‐arginine at two different temperatures, and with poly‐l‐lysine. Two approaches yield intrinsic binding constants which, depending on the model chosen, correspond to binding by sites with free neighbor sites or to direct interaction of nucleotides with the polyamino acid. The intrinsic binding constants obtained with poly‐l‐arginine depend upon the nature of the nucleotide base and, as is shown in the case of guanosine 5′ ‐phosphate, upon temperature. The corresponding value for guanosine monophosphate with poly‐l‐lysine is considerably smaller. It is pointed out that interaction of nucleotides with poly‐l‐arginine may be controlled by both the different stacking tendencies of the nucleotide bases and by the direct affinities between bases and polyamino acid. Copyright © 1969, Wiley Blackwell. All rights reserved