Stability constant of the 1:1 complex of sodium with guanosine 5'-monophosphate.

The stability of the 1:1 complex of sodium ion with the dianion of guanosine 5'-monophosphate has been determined by means of a potentiometric titration employing a specific ion electrode. The stability constant for the reaction Na(+) + 5'-GMP(2-) Na(5'-GMP)(-) was found to be 2.85 +/- 0.36 M(-1) at 5 degrees C and an ionic strength of 1.1 +/- 0.1 M. Although 5'-GMP forms ordered self-structures at high concentration in the presence of sodium ions, in dilute solution and at low sodium ion concentrations the Na(+) binding is weak and typical of that for other nucleotides.