Superprecipitation of an actomyosin-like complex isolated from Naegleria gruberi amoebae

A protein complex similar to muscle actomyosin and plasmodial myosin B has been isolated from Naegleria gruberi amoebae. This extract, which comprises approximately 0.7% of the total cell protein, has the solubility properties of actomyosin, displays Ca²⁺-activated, Mg²⁺-inhibited ATPase activity, forms microfilaments, and undergoes a strong superprecipitation reaction. Superprecipitation is initiated by ATP and is preceded by a very brief clearing phase. Although added Mg²⁺ is not essential for superprecipitation of the extract, the reaction proceeds maximally when 7 mM Mg²⁺ is provided. This extract does not appear to have a Ca²⁺ requirement, and superprecipitation is in fact inhibited by added Ca²⁺ ion at all concentrations greater than 0.1 mM. Both ATPase activity and superprecipitation of the actomyosin-like complex are inhibited by the sulfhydryl inhibitor salyrgan.