Adenosinetriphosphatase ( ATPase) has been demonstrated in a wide variety of animal and plant tissues. Among the protozoa, it is known to be present in Trypan-~sorna equiperdum, Colpodium campylum and Paramecium aurelia (Chen, '48; Seaman, '49; van Wagtendonk and Vloedman, Jr., '51; and Levine, '55). It has been demonstrated in the higher invertebrate tissues of ascidians, oysters, annelids, echinoderms and insects (Herrmann and Hartman, '48; Jaegar and Barth, '48; Humphrey, '49; van Thoai and Pin, '50); and in such diverse plants as bacteria and potatoes (Krishnan, '49; and Clark and MacLeod, '54).
Most of the preceding studies indicate that the enzyme in crude extracts is most active in the presence of Mg2+, or Ca2+, or both. A few studies indicate that MnZ+ can activate the enzyme. The literature is scanty concerning the ability of other divalent ions to stimulate the enzyme. Therefore, the aim of the present study is to determine (1) whether ATF'ase is present in s. pustulata; (2) whether certain divalent ions can serve as activators of the enzyme; ( 3 ) whether the stimulatory influence of a specific metal ion can be replaced by another; (4) whether the protozoan enzyme is similar in behavior to that of other animal tissues.