Antibody against the amino terminus of α-actin inhibits actomyosin interactions in the presence of ATP

Abstract

Actomyosin interactions in the presence of ATP were examined by using site-specific antibodies directed against the first seven N-terminal residues on skeletal α-actin. F ab fragments of these antibodies (SαN F ab) inhibited effectively the actin-activated ATPase of myosin subfragment 1 (S-1) at both 5 and 25 °C. Binding experiments carried out in the presence of ATP at 5 °C revealed that the catalytic inhibition was related to the inhibition of S-l binding to actin by F ab. At equimolar ratios of F ab to actin, the binding of S-1 to actin and the activated ATPase were inhibited by 75 and 82%, respectively. These results, when contrasted with the small effect of F ab on rigor actomyosin binding, suggest ATP-induced changes at the interface of actin and myosin.