title: Eosin, a fluorescent marker for the high-affinity ATP site of (K+ + H+)-ATPase.
abstract: Eosin has been used as a fluorescent probe for studying conformational states in (K+ + H+)-ATPase. The eosin fluorescence level is increased by Mg2+ (K0.5 = 0.2 mM). This increase is counteracted by K+ (I0.5 = 1.3 mM) and choline (I0.5 = 17.2 mM) and by ATP. Binding studies with eosin indicate that the increase and decrease in fluorescence is due to changes in binding of eosin to the enzyme. The Mg2+-induced specific binding has a Kd of 0.7 microM and a maximal capacity of 3.5 nmol per mg enzyme, which is equivalent to 2.5 site per phosphorylation site. These experiments and the fact that eosin competitively inhibits (K+ + H+)-ATPase towards ATP, suggest that eosin binds to ATP binding sites.
mesh_terms: D000251:Adenosine Triphosphatases / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000378:metabolism*; D000818:Animals; D001665:Binding Sites; D001667:Binding, Competitive; D002794:Choline / Q000494:pharmacology; D004801:Eosine Yellowish-(YS) / Q000378:metabolism*; D005456:Fluorescent Dyes; D005753:Gastric Mucosa / Q000201:enzymology; D017506:H(+)-K(+)-Exchanging ATPase; D008274:Magnesium / Q000494:pharmacology; D009994:Osmolar Concentration; D011188:Potassium / Q000494:pharmacology; D011487:Protein Conformation; D013050:Spectrometry, Fluorescence; D013552:Swine
chemical_list: D005456:Fluorescent Dyes; D000255:Adenosine Triphosphate; D000251:Adenosine Triphosphatases; D017506:H(+)-K(+)-Exchanging ATPase; D008274:Magnesium; D002794:Choline; D011188:Potassium; D004801:Eosine Yellowish-(YS)