Studies on (Na+ +K+) activated ATPase. XLI. Effects of N-ethylmaleimide on overall and partial reactions.
1. Preincubation with N-ethylmaleimide inhibits the overall activity of highly purified (Na+ +K+)-ATPase (ATP phosphohydrolase, EC 3.6.1.3) preparations of rabbit kidney outer medulla. 2. This inhibition is decreased by addition of ATP or 4-nitrophenylphosphate under non-phosphorylating conditions, and also by addition of ADP or adenylylimidodiphosphate. 3. N-ethylmaleimide treatment leads to inhibition of K+-stimulated 4-nitrophenylphosphatase activity, Na+-stimulated ATPase activity, and phosphorylation by ATP as well as by inorganic phosphate. These inhibitions strictly parallel that of the overal (Na+ +K+)-ATPase reaction. 4. N-ethylmaleimide lowers the number of sites which are phosphorylated by inorganic phosphate, without affecting the dissociation constant of the enzyme-phosphate complex. 5. N-ethylmaleimide does not affect the relative stimulation by ATP of the K+-stimulated 4-nitrophenylphosphatase activity. 6. These effects of N-ethylmaleimide can be explained as a complete loss of active enzyme, either by reaction of N-ethylmaleimide inside the active center, or by alterations in the quaternary structure through reactions outside the active center.
D009597:4-Nitrophenylphosphatase / Q000378:metabolism; D000244:Adenosine Diphosphate / Q000494:pharmacology; D000251:Adenosine Triphosphatases / Q000037:antagonists & inhibitors*; D000255:Adenosine Triphosphate / Q000494:pharmacology; D000266:Adenylyl Imidodiphosphate / Q000494:pharmacology; D000818:Animals; D001665:Binding Sites; D005033:Ethylmaleimide / Q000494:pharmacology*; D006863:Hydrogen-Ion Concentration; D007679:Kidney Medulla / Q000201:enzymology; D008274:Magnesium / Q000494:pharmacology; D008861:Microsomes / Q000201:enzymology; D010042:Ouabain / Q000494:pharmacology; D010710:Phosphates / Q000378:metabolism; D011188:Potassium / Q000378:metabolism / Q000494:pharmacology; D011817:Rabbits; D012964:Sodium / Q000378:metabolism
D010710:Phosphates; D000266:Adenylyl Imidodiphosphate; D010042:Ouabain; D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate; D012964:Sodium; D009597:4-Nitrophenylphosphatase; D000251:Adenosine Triphosphatases; D008274:Magnesium; D005033:Ethylmaleimide; D011188:Potassium