Extraction of Contractile Protein from Myxoamoebae of Physarum polycephalum

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Abstract
Contractile protein (myosin B) was isolated from myxoamoebae (haploid vegetative phase) of P. polycephalum. Myxoamoeba myosin B showed properties similar to those of natural actomyosin (myosin B) from muscle. Myxoamoeba myosin B appeared similar to myosin B of smooth muscle and non-muscle cells rather than to that of skeletal muscle, on the basis of quantitative characteristics and the presence of only 2 light chains. Myosin B isolated from myxoamoebae had almost the same properties as myosin B from plasmodia (diploid vegetative phase of Physarum). On SDS[sodium dodecyl sulfate]-gel electrophoresis, the plasmodium subunits were identical to actin and myosin subunits of myxoamoeba. The apparent particle length of myxoamoeba myosin B was 0.62-0.55 .mu.m, which was shorter than that of natural muscle actomyosin. Short length particles were also observed in plasmodium preparations. Some differences in ATPase activity were observed between myxoamoeba and plasmodium.