title: Identification of an essential sulfhydryl group in the ouabain binding site of (Na,K)-ATPase.
abstract: Ellman's reagent 5,5'-dithiobis-(2-nitrobenzoic acid) inhibits sodium- and potassium-stimulated ATPase, p-nitrophenyl phosphatase activity, and [3H]ouabain binding to lamb kidney (Na,K)-ATPase. The inactivation of [3H]ouabain binding follows pseudo-first order reaction kinetics at pH values less than or equal to 8.2. The inactivation of [3H]ouabain binding, but not of enzymatic activity, can be blocked by preincubation with ouabagenin, a rapidly reversible aglycone derivative of ouabain. The reduction in [3H]ouabain binding is due to a decrease in the number of binding sites rather than an alteration of the affinity of the enzyme for ouabain. Differential labeling at pH 8.2 with 1.0 mM 5,5'-dithiobis-(2-nitrobenzoic acid), preincubated with or without 5 microM ouabagenin, followed by tryptic digestion and reverse-phase high performance liquid chromatography of the generated soluble peptides reveals a single peptide labeled by the sulfhydryl probe that is protected by ouabagenin. From these results it is concluded that there is a single sulfhydryl group, essential for ouabain binding, presumably located in the ouabain binding site of lamb kidney (Na,K)-ATPase.
mesh_terms: D000818:Animals; D001665:Binding Sites; D004228:Dithionitrobenzoic Acid / Q000494:pharmacology; D007668:Kidney / Q000201:enzymology; D007700:Kinetics; D010042:Ouabain / Q000378:metabolism* / Q000494:pharmacology; D011485:Protein Binding; D012756:Sheep; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism*; D013438:Sulfhydryl Compounds; D014316:Tritium
chemical_list: D013438:Sulfhydryl Compounds; D014316:Tritium; D010042:Ouabain; D004228:Dithionitrobenzoic Acid; D000254:Sodium-Potassium-Exchanging ATPase