title: Ecto-ATPase of mammalian synaptosomes: identification and enzymic characterization.
abstract: Intact synaptosomes isolated from mammalian brain tissues (rat, mouse, gerbil, and human) have an ATP hydrolyzing enzyme activity on their external surface. The synaptosomal ecto-ATPase(s) possesses characteristics consistent with those that have been described for ecto-ATPases of various other cell types. The enzyme has a high affinity for ATP (the apparent Km values are in the range of 2-5 X 10(-5) M), and is apparently stimulated equally well by either Mg2+ or Ca2+ in the absence of any other cations. The apparent activation constant for both divalent cations is approximately 4 X 10(-4) M in all mammalian brain tissues studied. The involvement of a non-specific phosphatase in the hydrolysis of externally added ATP is excluded. ATP hydrolysis is maximal in the pH range 7.4-7.8 for both divalent cation-dependent ATPase activities. Dicyclohexylcarbodiimide, 2,4-dinitrophenol, trifluoperazine, chlorpromazine, and p-chloromercuribenzoate (50 microM) inhibit the ecto-ATPase, whereas ouabain (1 mM) and oligomycin (3.5 micrograms X mg-1 protein) show little or no inhibition of this enzyme activity. Inhibitor data suggest that the Mg2+- and Ca2+-dependent ecto-ATPase may represent two different enzymes on the surface of synaptosomes.
mesh_terms: D000251:Adenosine Triphosphatases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D001921:Brain / Q000201:enzymology* / Q000648:ultrastructure; D002118:Calcium / Q000494:pharmacology; D002413:Cations, Divalent; D002458:Cell Fractionation; D004789:Enzyme Activation / Q000187:drug effects; D005260:Female; D005849:Gerbillinae; D006801:Humans; D007700:Kinetics; D008274:Magnesium / Q000494:pharmacology; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D051381:Rats; D013379:Substrate Specificity; D013574:Synaptosomes / Q000201:enzymology*
chemical_list: D002413:Cations, Divalent; D000255:Adenosine Triphosphate; D000251:Adenosine Triphosphatases; C027201:ectoATPase; D008274:Magnesium; D002118:Calcium