Premium
The binding site of the strongly bound Eu 3+ in Eu 3+ ‐regenerated bacteriorhodopsin
Author(s) -
Sweetman L.L.,
El-Sayed M.A.
Publication year - 1991
Publication title -
febs letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.593
H-Index - 257
eISSN - 1873-3468
pISSN - 0014-5793
DOI - 10.1016/0014-5793(91)80531-7
Subject(s) - bacteriorhodopsin , deprotonation , protonation , proton , chemistry , fluorescence , halobacteriaceae , schiff base , mole , retinal , scatchard plot , photochemistry , crystallography , binding site , ion , physics , membrane , biochemistry , organic chemistry , quantum mechanics , halobacterium salinarum
A Scatchard plot for the strongly bound Eu 3+ to deionized bacteriorhodopsin (bR) was made using a method based on measuring the concentration of unbound Eu 3+ from its fluorescence intensity. The results suggest that the first mole of Eu 3+ added to a mole of bR is strongly bound by displacing 2–3 protons. In order to reconcile this result with the previous time‐resolved fluorescence studies on Eu 3+ ‐regenerated bR, which showed the pressence of 3 sites of comparable binding constants, one is forced to conclude that the emission from the strongly bound Eu 3+ is completely quenched, e.g. by energy transfer to the retinal. For this to take place, the Eu 3+ must be within a few A from the retinal, i.e. within the retinal pocket (the active site). The possible importance of this conclusion to the deprotonation mechanism of the protonated Schiff base, the switch of the proton pump in bR, is discussed.