title: The presence of two (Na+ + K+)-ATPase inhibitors in equine muscle ATP: vanadate nad a dithioerythritol-dependent inhibitor.
abstract: A potent inhibitor of (Na+ + K+)-ATPase activity was purified from Sigma equine muscle ATP by cation- and anion-exchange chromatography. The isolated inhibitor was identified by atomic absorption spectroscopy and proton resonance spectroscopy to be an inorganic vanadate. The isolated vanadate and a solution of V2O5 inhibit sarcolemma (Na+ + K+)-ATPase with an I50 of 1 micrometer in the presence of 1 mM ethyleneglycol-bis-(beta-aminoethylether)-N,N'-tetraacetic acid (EGTA), 145 mM NaCl, 6mM MgCl2, 15 mM KCl and 2 mM synthetic ATP. The potency of the isolated vanadate is increased by free Mg2+. The inhibition is half maximally reversed by 250 micrometer epinephrine. Equine muscle ATP was also found to contain a second (Na+ + K+)-ATPase inhibitor which depends on the sulfhydryl-reducing agent dithioerythritol for inhibition. This unknown inhibitor does not depend on free Mg2+ and is half maximally reversed by 2 micrometer epinephrine. Prolonged storage or freeze-thawing of enzyme preparations decreases the susceptibility of the (Na+ + K+)-ATPase to this inhibitor. The adrenergic blocking agents, propranolol and phentolamine, do not block the catecholamine reactivation. The inhibitors in equine muscle ATP also inhibit highly purified (Na+ + K+)-ATPase from shark rectal gland and eel electroplax. The inhibitors in equine muscle ATP have no effect on the other sarcolemmal ATPases, Mg2+-ATPase, Ca2+-ATPase and (Ca2+ + Mg2+)-ATPase.
mesh_terms: D000251:Adenosine Triphosphatases / Q000037:antagonists & inhibitors*; D000255:Adenosine Triphosphate / Q000032:analysis*; D000818:Animals; D004226:Dithioerythritol; D006736:Horses; D009132:Muscles / Q000032:analysis*; D009206:Myocardium / Q000032:analysis; D011188:Potassium; D011817:Rabbits; D012508:Sarcolemma / Q000032:analysis; D012964:Sodium; D014639:Vanadium / Q000032:analysis*
chemical_list: D014639:Vanadium; D004226:Dithioerythritol; D000255:Adenosine Triphosphate; D012964:Sodium; D000251:Adenosine Triphosphatases; D011188:Potassium