title: Inhibitory characteristics of 3,5-dibromo-1-acetoxy-4-oxo-2,5-cyclohexadien-1-acetonitrile, a semisynthetic derivative of aeroplysinin-1 from sponges (Aplysinidae), on Na+ - K+-ATPase.
abstract: 3,5-Dibromo-1-acetoxy-4-oxo-2,5-cyclohexadien-1-acetonitrile (dienone A) inhibited Na+ - K+-ATPase with a half-maximal inhibition concentration (I50) equal to 2.9 X 10(-6)M. Inhibition was time- and pH-dependent and complete after 20-30 min preincubation within a range of pH from 7.0 to 9.0. Kinetic evaluation of the cationic substrate activation of Na+ - K+-ATPase indicated mixed type inhibition with regard to Na+ and K+ and competitive inhibition with regard to ATP activation of the enzyme. The presence of Mg2+ caused an increased inhibition. Also, K+-p-nitrophenyl phosphatase activity was altered by dienone A and mixed type inhibition with regard to p-nitrophenyl phosphate and K+ was demonstrated. Inhibition was partially restored by repeated washing. Preincubation with sulfhydryl reagents protected the enzyme from inhibition. A significant linear correlation between reactive enzyme sulfhydryl contents [SH] and Na+ - K+-ATPase activity in the presence of varying concentrations of dienone A was observed. One of the factors causing cytotoxic activity of this compound might be its interaction with some thiol groups of the membrane-bound Na+ - K+-ATPase.
mesh_terms: D009597:4-Nitrophenylphosphatase / Q000378:metabolism; D000097:Acetonitriles / Q000494:pharmacology*; D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D053138:Cyclohexenes; D004789:Enzyme Activation / Q000187:drug effects; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D007700:Kinetics; D008274:Magnesium / Q000494:pharmacology; D011161:Porifera; D011188:Potassium / Q000494:pharmacology; D051381:Rats; D012964:Sodium / Q000494:pharmacology; D000254:Sodium-Potassium-Exchanging ATPase / Q000037:antagonists & inhibitors*; D013439:Sulfhydryl Reagents / Q000494:pharmacology
chemical_list: D000097:Acetonitriles; D053138:Cyclohexenes; D013439:Sulfhydryl Reagents; C042151:aeroplysinin I; C042150:dienone A; D000255:Adenosine Triphosphate; D012964:Sodium; D009597:4-Nitrophenylphosphatase; D000254:Sodium-Potassium-Exchanging ATPase; D008274:Magnesium; D011188:Potassium