CONTRACTILE BASIS OF AMEBOID MOVEMENT .2. STRUCTURE AND CONTRACTILITY OF MOTILE EXTRACTS AND PLASMALEMMA ECTOPLASM GHOSTS

The role of Ca and Mg-ATP on the structure and contractility in motile extracts of Amoeba proteus and plasmalemma-ectoplasm ghosts of Chaos carolinensis was investigated by correlating light microscopic and EM observations with turbidity and birefringence measurements. The extract is nonmotile and contains very few F-actin filaments and myosin aggregates when prepared in the presence of low Ca2+ and ATP concentrations at an ionic strength of I = 0.05, pH 6.8. The addition of 1.0 mM MgCl2, 1.0 mM ATP, in the presence of a low Ca2+ concentration (relaxation solution) induced the formation of some fibrous bundles of actin without contracting, whereas the addition of a micromolar concentration of Ca in addition to 1.0 mM-ATP (contraction solution) (Taylor et al, 1973) initiated the formation of large arrays of F-actin filaments followed by contractions. Plasmalemma-ectoplasm ghosts prepared in the relaxation solution exhibited very few straight F-actin filaments and myosin aggregates. In contrast, plasmalemma-ectoplasm ghosts treated with contraction solution contained many straight F-actin filaments and myosin aggregates. The increase in the structure of ameba cytoplasm at the endoplasm-ectoplasm interface can be explained by a combination of the transformation of actin from a less filamentous to a more structured filamentous state, possibly involving the cross-linking of actin to form fibrillar arrays (see above-mentioned reference) followed by contractions of the actin and myosin along an undetermined distance of the endoplasm and/or ectoplasm.