Similar affinities of ADP and ATP for G‐actin at physiological salt concentrations

Abstract
The equilibrium constant for the exchange of ATP and ADP at G‐actin was determined by fluorimetric titration of G‐actin‐bound ε‐ATP by ATP or ADP. The affinity of ATP for G‐actin was found to be only about 3‐fold higher than the affinity of ADP for G‐actin at 37°C, pH 7.5 and physiologically relevant salt concentrations (100 mmol K+/l, 0.8 mmol Mg2+/l, 2+/l).