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  • Title: Purification and characterization of a Ca2+/Mg2+ ecto-ATPase from rat heart sarcolemma.
    Author: Tuana BS, Dhalla NS.
    Journal: Mol Cell Biochem; 1988 May; 81(1):75-88. PubMed ID: 2971873.
    Abstract:
    The Ca2+/Mg2+ ATPase of the rat heart sarcolemmal particles was solubilized with Triton X-100 after treating the membranes with trypsin and purified by high speed centrifugation, ammonium sulfate fractionation, hydrophobic chromatography and gel filtration. The purified enzyme was seen as a single protein band in non-denaturing polyacrylamide gel electrophoresis and its molecular weight by gel filtration was found to be about 240,000. The enzyme utilized Ca-ATP or Mg-ATP as a substrate with high affinity sites (Km = 0.12-0.16 mM) and low affinity sites (Km = 1 mM). The enzyme also utilized CTP, GTP, ITP, UTP and ADP as substrates but at a lower rate in comparison to ATP. The enzyme was activated by Ca2+ (Ka = 0.4 mM) and Mg2+ (Ka = 0.2 mM) as well as by other cations in the order Ca2+ greater than Mg2+ greater than Mn2+ greater than Sr2+ greater than Ba2+ greater than Ni2+ greater than Cu2+. The ATPase activity in the presence of Ca2+ was markedly inhibited by Mg2+, Mn2+, Ni2+ and Cu2+ whereas the monovalent cations such as Na+ and K+ were without effect. The enzyme did not exhibit Ca2+ stimulated Mg2+ dependent ATPase activity and was insensitive to calmodulin, ouabain, verapamil, D-600, oligomycin, azide and vanadate. Optimum pH for Ca2+ or Mg2+ ATPase activity was 8.5-9.0. In view of the possible ectoenzyme nature of the ATPase, its role in adenine nucleotide and Ca2+ metabolism in the myocardium is discussed.
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