title: The position of the ATP binding site on the (Ca2+ + Mg2+)-ATPase.
abstract: We present a convenient method to calculate the efficiency of fluorescence energy transfer in two-dimensional membrane systems. We apply it to the analysis of energy transfer between phospholipid molecules labelled with fluorescein and rhodamine groups, and of energy transfer in reconstituted membranes containing (Ca2+ + Mg2+)-ATPase purified from sarcoplasmic reticulum, with the ATPase labelled at the ATP binding site with fluorescein as donor, and rhodamine-labelled lipid as acceptor. The ATP binding site is found to be distant from the plane of the lipid/water interface of the membrane. It is suggested that the ATPase is present in the membrane as a dimer, with the two ATP binding sites in the dimer being close to the protein/protein interface. Addition of vanadate causes no change in quenching, suggesting that the ATP binding site does not move significantly with respect to the lipid/water interface in the E1-E2 conformational transition of the ATPase.
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism*; D000818:Animals; D001665:Binding Sites; D017301:Ca(2+) Mg(2+)-ATPase / Q000378:metabolism*; D000252:Calcium-Transporting ATPases / Q000378:metabolism*; D004735:Energy Transfer; D005260:Female; D016650:Fluorescein-5-isothiocyanate; D005452:Fluoresceins; D008433:Mathematics; D011817:Rabbits; D012235:Rhodamines; D013861:Thiocyanates
chemical_list: D005452:Fluoresceins; D012235:Rhodamines; D013861:Thiocyanates; D000255:Adenosine Triphosphate; D017301:Ca(2+) Mg(2+)-ATPase; D000252:Calcium-Transporting ATPases; D016650:Fluorescein-5-isothiocyanate