title: Characteristics of skeletal muscle ecto-ATPase in situ.
abstract: The properties of a cell surface nucleoside 5'-triphosphatase have been studied in small, intact, frog skeletal muscles, as a means of distinguishing the enzyme from other adenosine 5'-triphosphatases and of understanding its behaviour in the muscle membrane. The ectoenzyme in situ was shown to be a Ca2+- or Mg2+-activated ATPase liberating 7.5 +/- 0.4 (mean +/- SEM, n = 30) mumol of inorganic phosphate/g of muscle per 20 min, when the muscle was exposed to 2 mM ATP and 2 mM Ca2+ in Ringer's solution. The apparent Km for Mg2+ was 0.74 mM and for Ca2+ was 0.23 mM. A residual ATPase activity (20%) was found in the complete absence of divalent cations suggesting the existence of two ATPase types. A broad specificity toward nucleoside 5'-triphosphates was exhibited by the ecto-ATPase, but there was no nonspecific phosphatase activity. The enzyme was inhibited by La3+ and Cd2+, but was insensitive to ouabain, 2,4-dinitrophenol, oligomycin, and ruthenium red. Thus the ectoenzyme was not a Na+, K+-transport ATPase, was not an ATPase of mitochondrial origin, or a Ca2+-transport enzyme. Insulin had no effect. Inhibition by mersalyl, carbodiimide, and polar and cross-linking nonpolar nitrobenzene derivatives suggested that, for maximum activity, this membrane-bound enzyme required free sulfhydryl groups, certain free carboxyls, and an appreciable degree of hydrophobicity in its microenvironment.
mesh_terms: D009597:4-Nitrophenylphosphatase / Q000378:metabolism; D000251:Adenosine Triphosphatases / Q000378:metabolism*; D000818:Animals; D002118:Calcium / Q000378:metabolism; D004139:Dinitrofluorobenzene / Q000494:pharmacology; D007328:Insulin / Q000494:pharmacology; D007811:Lanthanum / Q000494:pharmacology; D008274:Magnesium / Q000378:metabolism; D009132:Muscles / Q000201:enzymology*; D009711:Nucleotides / Q000378:metabolism; D011894:Rana pipiens; D014302:Trinitrobenzenesulfonic Acid / Q000494:pharmacology
chemical_list: D007328:Insulin; D009711:Nucleotides; D007811:Lanthanum; D014302:Trinitrobenzenesulfonic Acid; D004139:Dinitrofluorobenzene; D009597:4-Nitrophenylphosphatase; D000251:Adenosine Triphosphatases; C027201:ectoATPase; D008274:Magnesium; D002118:Calcium