Characterization and localization of an ATP diphosphohydrolase activity (EC 3.6.1.5) in sarcolemmal membrane from rat heart

摘要: In the present report we describe an ATP diphosphohydrolase (apyrase EC 3.6.1.5) in rat cardiac sarcolemma. It is Ca2+ dependent and insensitive to ouabain, orthovanadate, N-ethylmaleimide (NEM), lanthanum, oligomycin that are classical ATPase inhibitors. Sodium azide a mitochondrial inhibitor at low concentrations, did not affect enzyme activity 5.0 mM or below. contrast, high concentrations (> 10 mM) sodium inhibited enzyme. Levamisole, specific of alkaline phosphatase P1, P5-di(adenosine 5′-)pentaphosphate (Ap5A), adenylate kinase inhibit Mercury chloride showed parallel inhibition hydrolysis both substrates apyrase. Similar profiles powerful evidence for common catalytic site substrates. The has optimum pH range 7.5–8.0 catalyzes triphospho- diphosphonucleosides other than ADP. apparent Km (Michaelis constant) Vmax (maximal velocity) 62.1 ± 5.2 μM 1255.7 178 μmol inorganic phosphate liberated/min/mg with 59.4 4.3 269.2 39 Enzyme markers indicated this apyrase associated plasma membrane. A deposition lead granules on outer surface sarcolemmal vesicles was observed by electron microscopy presence either ADP as substrate. suggested could regulate concentration extracellular adenosine, thus important control vascular tone coronary flow.