Interaction of Adenylosuccinate Synthetase with F-Actin

Both crude and purified preparations of adenylosuccinate synthetase from muscle were found to combine with, and dissociate from, muscle debris precipitated from a homogenate of the muscle with water. The binding and dissociation depended on ionic strength. Further study showed that the muscle enzyme was adsorbed to F-actin, but not to G-actin or myosin. The muscle-type enzyme from the liver also associated with F-actin, but the liver-type enzyme from the liver did not. In the absence of KCl the molar ratio of adenylosuccinate synthetase from skeletal muscle to actin monomer in F-actin in the complex formed was 1 to 4. From a Scatchard plot the dissociation constant was calculated to be 0.72 micrometer. The binding was maximal at pH 5.5-7 in 30 mM potassium phosphate buffer. The complex was completely dissociated in the presence of 0.21 M KCl. The physiological significance of this binding is discussed on the basis of these findings.