Membrane-bound ATPase in chloroplasts of Euglena gracilis.

Membrane-bound ATPase activities in chloroplasts of Euglena were examined. Ca2+- and Mg2+-dependent activities were relatively high in membrane preparations and could not be further activated by a number of procedures. The enzyme was found to be highly specific for purine nucleotides and was inhibited by the usual inhibitors of photophosphorylation. Km values of Ca2+ and Mg2+ ATPase for ATP were 2.5 and 2.1 mM, respectively. Both activities were competitively inhibited by ADP and inorganic phosphate. A relationship was found between Ca2+- or Mg2+-dependent ATPase activities and chloroplast completeness. The possibilities that these activities result from one enzyme depending on Ca2+ or Mg2+ or from two different enzymes are discussed.