Interaction of Adenylosuccinate Synthetase with F‐Actin

Abstract

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 μM. 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.