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.
D000251:Adenosine Triphosphatases / Q000378:metabolism*; D002118:Calcium / Q000494:pharmacology; D002462:Cell Membrane / Q000187:drug effects / Q000201:enzymology / Q000648:ultrastructure; D002736:Chloroplasts / Q000187:drug effects / Q000201:enzymology* / Q000648:ultrastructure; D004789:Enzyme Activation / Q000187:drug effects; D005056:Euglena gracilis / Q000201:enzymology*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008274:Magnesium / Q000494:pharmacology; D010785:Photophosphorylation / Q000187:drug effects; D013696:Temperature
D000251:Adenosine Triphosphatases; D008274:Magnesium; D002118:Calcium