Abstract
Adenosine triphosphatase (ATPase) inactivation of squid myosin subfragment-1 (S-1) was strongly suppressed upon addition of adenylimidophosphate (AMPPNP), an analogous compound of adenosine triphosphate (ATP); whereas suppression by adenosine diphosphate (ADP) and pyrophosphate (PPi) was not as effective. Adenylimidophosphate did not stabilize myofibrils in which myosin is stabilized by F-actin. Thus, the stabilization effect by F-actin and AMPPNP is not additive. Pyrophosphate markedly accelerated the inactivation of myofibrils through the loss of protection by F-actin. The suppressive effect of F-actin on myosin ATPase inactivation was much greater than that by AMPPNP. The stabilization effects of AMPPNP and F-actin on S-1 were almost completely lost when the medium contained approximately 1 M KCl.
