title: The binding of ATP to the catalytic and the regulatory site of Ca2+, Mg2+-dependent ATPase of the sarcoplasmic reticulum.
abstract: Two kinds of ATP binding sites were found on the ATPase molecule in deoxycholic acid-treated sarcoplasmic reticulum. One was the catalytic site (1 mol/mol active site) and its affinity was high. Upon addition of Ca2+, all the ATP bound to the catalytic site disappeared at 75 mM KCl, while a significant amount of ATP remained bound to the site at 0-2 mM KCl. The latter binding was found to be due to the formation of a slowly exchanging enzyme--ATP complex, which is in equilibrium with phosphoenzyme + ADP. The other binding site was the regulatory one (1 mol/mol active site) and its affinity was low, changing only insignificantly upon addition of Ca2+. The ATP binding to the regulatory site shifted the equilibrium between the slowly exchanging complex and EP toward EP.
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism*; D017301:Ca(2+) Mg(2+)-ATPase; D000252:Calcium-Transporting ATPases / Q000378:metabolism*; D066298:In Vitro Techniques; D007700:Kinetics; D011189:Potassium Chloride / Q000494:pharmacology; D012519:Sarcoplasmic Reticulum / Q000201:enzymology*
chemical_list: D011189:Potassium Chloride; D000255:Adenosine Triphosphate; D017301:Ca(2+) Mg(2+)-ATPase; D000252:Calcium-Transporting ATPases