The Isolation of Myxomyosin, an Atp- Sensitive Protein from the Plasmodium of a Myxomycete* by Paul O.p. Ts'o, Luther Eggman, and Jerome Vinograd

The plasmodium of the slime mold, Physarum polycephalura, has been extensively used as a model organism in studies of protoplasmic streaming (1). Recently both streaming in the living plasmodium and the viscosity of suitably prepared plasmodial extracts have been shown to respond specifically to additions of ATP. The plasmodla exhibit increased streaming (2), whereas the extracts become less viscous (2, 3). The change in viscosity is transient; during the recovery phase ATP is destroyed and inorganic phosphate released. This cycle may be repeated several times as with actomyosin (15, 16). The previously reported separation of the cytoplasmic extract into active and inactive fractions by ammonium sulfate precipitation (2) suggested that further effort might yield active concentrates suitable for studying the mecha~nism of the ATP-induced changes in viscosity, and the relation of this reaction to the mechanism of protoplasmic streaming. The present paper deals with the method of isolation of the active material and some of its physical and chemical characteristics.