title: Ca2+-sensitivity of actomyosin ATPase purified from Physarum polycephalum.
abstract: A contractile protein closely resembling natural actomyosin (myosin B) of rabbit skeletal muscle was extracted from plasmodia of the slime mold, Physarum polycephalum, by protecting the SH-groups with beta-mercaptoethanol or dithiothreitol. Superprecipitation of the protein induced by Mg2+-ATP at low ionic strength was observed only in the presence of very low concentrations of free Ca2+ ions, and the Mg2+-ATPase [EC 3.6.1.3] reaction was activated 2- to 6-fold by 1 muM of free Ca2+ ions. Crude myosin and actin fractions were separated by centrifuging plasmodium myosin B in the presence of Mg2+-PPi at high ionic strength. The crude myosin showed both EDTA- and Ca2+-activated ATPase activities. The Mg2+-ATPase activity of crude myosin from plasmodia was markedly activated by the addition of pure F-actin from rabbit skeletal muscle. Addition of the F-action-regulatory protein complex prepared from rabbit skeletal muscle as well as the actin fraction of plasmodium caused the same degree of activation as the addition of pure F-actin only in the presence of very low concentrations of Ca2+ ion
mesh_terms: D000205:Actomyosin / Q000378:metabolism*; D000251:Adenosine Triphosphatases / Q000302:isolation & purification / Q000378:metabolism*; D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D004229:Dithiothreitol; D004789:Enzyme Activation / Q000187:drug effects; D007700:Kinetics; D008623:Mercaptoethanol; D009132:Muscles / Q000378:metabolism; D009218:Myosins / Q000302:isolation & purification / Q000378:metabolism; D009235:Myxomycetes / Q000201:enzymology*; D009994:Osmolar Concentration; D010804:Physarum / Q000201:enzymology*; D011817:Rabbits; D013045:Species Specificity
chemical_list: D008623:Mercaptoethanol; D000205:Actomyosin; D000251:Adenosine Triphosphatases; D009218:Myosins; D002118:Calcium; D004229:Dithiothreitol