The 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°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.