The "Contractile" Proteins of Acanthamoeba castellanii

The goal of our research is to understand the molecular and ultrastructural events responsible for the type of cellular movements characteristic of amebae and which occur in virtually all other living cells. Our approach has been to identify, purify, and characterize the presumptive “contractile” proteins of the small soil ameba, Acanthamoeba castellanii. We have found that the contractile proteins of this primitive cell share many important properties with muscle actin and myosin, but also that significant differences exist, especially in the myosin. These results, taken together with those of others on the slime mold Physarum polycephalmn (Hatano and Oosawa, 1966; Adelman and Taylor, 1966a, b; Hatano and Ohnuma, 1970; Nachmias et al., 1970; Nachmias, 1972) and platelets (Adelstein et al., 1971; Behnke et al., 1971; Zucker-Franklin and Grusky, 1972), suggest that the actin-myosin based contractile mechanism of muscle is a highly specialized example of a widely distributed fundamental mechanism for...