Electron Microscopic Identification of Actin Associated with Isolated Amoeba Plasma Membranes

Abstract Plasma membranes isolated from Acanthamoeba castellanii are associated with filaments that have been identified as actin by the width of the filaments, their specific interaction with heavy meromyosin to form polarized arrowhead structures, and their removal by conditions that dissociate actin. Some evidence was obtained that the co-isolation of plasma membranes and actin might be a consequence of specific attachment of the filaments to the cytoplasmic surface of the membrane in vitro and, by inference, in vivo.