The plasmodia of the slime mold, Physarum polycephalum, is a classical material for studies of the structure of protoplasm and the mechanism of protoplasmic streaming. Observations of Marsland (12), Lewis (10), Camp (4), and others have shown that the protoplasm possesses a gel structure which may be reversibly transformed into a sol. The work reported in the present paper developed from considerations of this phenomenon and of how a cell might use it to transform chemical energy into mechanical work such as protoplasmic streaming.Pkysarum has a shuttle type of protoplasmic streaming which changes direction rhythmically, the rate of flow ranging from zero to about 1.0 ram. per second (8). The motivating force, measured in terms of the hydrostatic pressure just sufficient to stop the protoplasmic flow, is of the order of 6 to 15 cm. of water (8). The flow is apparently powered by respiratory metabolism since agents such as dinitrophenol (DNP) which uncouple phosphorylative transfer from respiration inhibit streaming (18). This implies that the energy required for streaming is supplied as adenosinetdphosphate (ATP). The importance of ATP in streaming is more directly indicated by the findings of Goldacre and Lorch (7), and of Kfiszat (9) that microinjection of ATP into ameba specifically increases the rate of protoplasmic flow. What then is the component of cytoplasm which responds to ATP? Loewy (11) has demonstrated that crude extracts of Pkysarum polycephalum plasmodia undergo reversible changes in viscosity in response to additions of ATP, and that inorganic phosphate is liberated in the process. In this respect, the behavior of the plasmodial extract is similar to that of an actomyosin preparation from muscle tissue.The present paper concerns the nature of the ATP response of myxomycete protoplasmic extracts. Procedures for measuring the ATP response of the material are established. This information is then employed to develop a procedure for isolating the active component from the crude extract.
1. A procedure has been developed for the preparation of an active concentrate from the myxomycete, Physarum polycephalum. This concentrate responds with a lowered viscosity to the addition of small amounts of ATP. The preparation recovers in viscosity, and the process may be repeated.
2. In the most active concentrates, 75 per cent of the non-dialyzable material moves as a single boundary both in the descending limb in electrophoresis and in the ultracentrifuge. It contains about 10 per cent ribonucleic acid, which is at least in part reversibly bound to the protein.
3. The active material has been designated myxomyosin because of its origin and its similarity to actomyosin in ATP response.
Sept. 20, 1955 pH Effect on the Reaction between Ovalbumin and its Rabbit Antibodies 4855 unsuspected fundamental similarities in the mechanism of reaction between many or all natural protein antigens and their antibodies. In both systems, we have demonstrated2^3 that a single ionized carboxyl group is essentially involved in every Ag-Ab bond, and that a positively charged group is presumably present on the complementary site. The positive standard entropy change is attributed to the release of bound, or polarized, water from the charged sites upon bond formation. The near athermicity of these reactions14 indicates that (14) A calorimetric value of AH = -40 kcal./mole foi the reaction between hemocyanin and its antibodies has been reported.15 This large enthalpy change, however, might be due in part to dissociative equilibria exhibited by hemocyanin,16 and should be confirmed.(15) W.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.