<p> Amoeboid Motion is thought to be due to the action of an actomyosin- like protein present in the cytoplasm of amoeba. A co-ordinated net- 0 work of microfilaments of the actomyosin-like protein, 70 A in diameter, may be the mechanical means of accomplishing amoeboid motion. The microfilaments formed of the actomyosin-like protein, may be capable of rapid association and dissociation in vivo. In this thesis, the cytoplasm of Naegleria gruberi amoeba has been shown to possess a protein similar to actomyosin. Characterization of the ATPase activity, superprecipitating ability, electrophoretic behaviour and microfilament producing ability reveal that the actomyosin-like protein of Naegleria gruberi amoeba is quite similar to the analogous protein in Physarum polycephalum. Naeqleria gruberi may be an ideal organism in which to study the interconversion of one form of a biologically active macromolecule to another., In different stages of the life cycle, amoeboid motion, flagellar beating and mitotic spindles are present. It is possible that the same contractile molecules in different forms may perform different functions. </P> / Thesis / Master of Science (MSc)