title: Inhibition of N-ethylmaleimide of the MgATP-driven proton pump of the chromaffin granules.
abstract: The thiol reagent N-ethylmaleimide (NEM) completely inhibits the proton pump activity of the H+-ATPase in chromaffin granule 'ghosts' at concentrations which only partly (approximately 20%) inhibit the Mg2+-dependent ATP hydrolysis. Half-maximal inhibition was obtained at approximately 13 microM NEM as compared to 18 microM for the classical proton channel inhibitor N,N'-dicyclohexylcarbodiimide (DCCD), and the apparent stoichiometry of the inhibitors at complete inhibition was NEM : DCCD congruent to 1 : 2. HIgh concentrations of NEM (greater than 100 microM) induce a dissipation of the transmembrane potential generated by MgATP. These findings establish NEM as a valuable proton channel inhibitor in chromaffin granules and explain the rather complex effect of NEM previously reported for catecholamine accumulation in this organelle.
mesh_terms: D000251:Adenosine Triphosphatases / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000494:pharmacology*; D000311:Adrenal Glands / Q000201:enzymology; D000818:Animals; D002417:Cattle; D002837:Chromaffin Granules / Q000187:drug effects / Q000201:enzymology*; D002838:Chromaffin System / Q000201:enzymology*; D005033:Ethylmaleimide / Q000494:pharmacology*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D006180:Proton-Translocating ATPases
chemical_list: D000255:Adenosine Triphosphate; D000251:Adenosine Triphosphatases; D006180:Proton-Translocating ATPases; D005033:Ethylmaleimide