Abstract
Membrane-bound ATPase activities in chloroplasts of Euglena were examined. Ca 2+- and Mg 2+-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. K m values of Ca 2+ and Mg 2+ 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 Ca 2+- or Mg 2+-dependent ATPase activities and chloroplast completeness. The possibilities that these activities result from one enzyme depending on Ca 2+ or Mg 2+ or from two different enzymes are discussed.
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