[Effect of phalloidin on the contractile structures in cytoplasmic preparations of Amoeba proteus].

The effect of phalloidin on ultrastructural components involved in movement have been studied in spread cytoplasmic preparations of Amoeba proteus. In absence of phalloidin, actin filaments are usually rare and only myosin rods are observed. With concentrations of phalloidin between 2 X 10(-6) M and 5 X 10(-6) M, numerous F-actin filaments are present in the preparations. Most of these actin filaments are straight, however some appeared branched and interconnected. Higher concentrations of phalloidin inhibit the movement of naked cytoplasm. Fibrils composed by aggregation of F-actin filaments are present in these preparations. Myosin rods are unaffected by phalloidin.