Extraction of an actin‐like protein from the plasmodium of a myxomycete and its interaction with myosin a from rabbit striated muscle

An actin‐like protein was obtained from the plasmodia of a myxomycete, Physarum polycephalum . It forms a complex with muscle myosin A which behaves similarly to the actomyosin from rabbit striated muscle. On the addition of ATP the complex of this protein with myosin A shows a viscosity drop at high concentrations of KCl (∼0.5 M). At low concentrations of KCl (∼0.05 M) this complex superprecipitates from solutions containing 1 mM MgCl 2 and shows Mg‐activated ATPase activity. That is, the actin‐like protein converts the ATPase of myosin A to the actomyosin type.