STUDIES ON (NA+-K+)-ACTIVATED ATPASE .23. A MG2+-ATPASE IN ESCHERICHIA COLI ACTIVATED BY MONOVALENT CATIONS

1. 1. The properties of a Mg2+-activated ATPase (ATP phosphohydrolase, EC 3.6.1.4) with optimum pH 8.7 in Escherichia coli, strain K-12, are described. 2. 2. Addition of KCl increases the specific activity over the entire pH range. 3. 3. Various monovalent cations, added as chlorides, have a different activating effect. 4. 4. Of all phosphates tested, ADP is the best substrate next to ATP, and of all bivalent cations tested, Mg2+ is the best cofactor for this phosphatase activity. 5. 5. The optimal temperature for the Mg2+-ATPase activity is 45°, both in the presence and in the absence of KCl. 6. 6. Disintegration of the bacteria by sonication leads to a loss of the activating effect of monovalent cations on the Mg2+-ATPase activity. 7. 7. In the light of these properties of the Mg2+-ATPase, the occurrence of a (Na+-K+)-ATPase system in E. coli was reinvestigated and confirmed. © 1969.