title: Metal ion binding sites of bacteriorhodopsin. Laser-induced lanthanide luminescence study.
abstract: Laser-excited luminescence lifetimes of lanthanide ions bound to bacteriorhodopsin have been measured in deionized membranes. The luminescence titration curve, as well as the binding curve of apomembrane (retinal-free) with Eu3+, has shown that the removal of the retinal does not significantly affect the affinity of Eu3+ for the two high affinity sites of bacteriorhodopsin. The D2O effects on decay rate constants indicate that Eu3+ bound to the high affinity sites of native membrane or apomembrane is coordinated by about six ligands in the first coordination sphere. Tb3+ is shown to be coordinated by four ligands. The data indicate that metal ions bind to the protein with a specific geometry. From intermetal energy transfer experiments using Eu3+-Pr3+, Tb3+-Ho3+, and Tb3+-Er3+, the distance between the two high affinity sites is estimated to be 7-8 A.
mesh_terms: D001436:Bacteriorhodopsins / Q000378:metabolism*; D003903:Deuterium; D005063:Europium; D006217:Halobacterium; D007834:Lasers; D008163:Luminescent Measurements; D008433:Mathematics; D008670:Metals / Q000378:metabolism*; D008674:Metals, Rare Earth
chemical_list: D008670:Metals; D008674:Metals, Rare Earth; D005063:Europium; D001436:Bacteriorhodopsins; D003903:Deuterium