title: ATP synthesis by Ca2+ + Mg2+-ATPase in detergent solution at constant Ca2+ levels.
abstract: ATP has been synthesized by the purified Ca2+ + Mg2+-dependent ATPase from sarcoplasmic reticulum (SR) solubilized in nonionic detergent dodecyloctaoxyethylenglycol-monoether in a solution containing inorganic phosphate and glycerol by changing pH upon addition of ADP. The Ca2+ concentration is kept constant during the experiment. Optimum synthesis is found at CaCl2 = 0.6 mM and the delta pH = 2.9 +/- 0.2. The enzyme has been digested by trypsin for 1 and 20 min, and it is found that synthesis of ATP is correlated with the Ca2+-uptake into SR. The data indicate that the enzyme alone is responsible for active transport of Ca2+ in SR. The driving force for the ATP synthesis of the process may be due to various ion-protein interactions. H+ cannot substitute for Ca2+ in the synthesis of ATP but acts probably through a modification of the Ca2+ binding sites. The data give support that the integrity of the enzyme molecule between its hydrolytic site and the Ca2+-binding sites is essential for the overall Ca2+ transport.
mesh_terms: D000255:Adenosine Triphosphate / Q000096:biosynthesis*; D000818:Animals; D017301:Ca(2+) Mg(2+)-ATPase; D002118:Calcium / Q000494:pharmacology*; D000252:Calcium-Transporting ATPases / Q000378:metabolism*; D007700:Kinetics; D009132:Muscles / Q000201:enzymology; D010446:Peptide Fragments / Q000032:analysis; D011817:Rabbits; D012519:Sarcoplasmic Reticulum / Q000201:enzymology*; D014357:Trypsin
chemical_list: D010446:Peptide Fragments; D000255:Adenosine Triphosphate; D014357:Trypsin; D017301:Ca(2+) Mg(2+)-ATPase; D000252:Calcium-Transporting ATPases; D002118:Calcium