Connectin, an elastic protein of muscle. A connectin-like protein from the plasmodium Physarum polycephalum

A completely sodium dodecyl sulfate-insoluble protein was obtained from plasmodia of Physarum polycephalum. The amino acid composition of this protein was very similar to that of connectin, an elastic protein of muscle. When the protein suspension was treated with 6 M guanidine-HCl in the presence of 0.1 M 2-mercaptoethanol, entanglements of very thin filaments, less than 5 nm in width, were observed under an electron microscope. Since the network structure is almost the same as that of isolated muscle connectin, this plasmodium protein can be regarded as forming an elastic net structure. Using an antiserum against the insoluble protein, it appeared to be located at the peripheral region of the plasmodium. This elastic net structure may act as a cytoskeleton at the cytoplasmic surface of the plasmodium cell membrane.