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The surface potential on the purple membrane measured using a modified bacteriorhodopsin chromophore as the spectroscopic probe
Author(s) -
Ehrenberg Benjamin,
Ebrey Thomas G.,
Friedman Noga,
Sheves Mordechai
Publication year - 1989
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(89)80715-x
Subject(s) - bacteriorhodopsin , chromophore , chemistry , halobacterium , divalent , retinal , membrane , pigment , surface charge , charge density , electrolyte , analytical chemistry (journal) , photochemistry , chromatography , organic chemistry , biochemistry , physics , quantum mechanics , electrode
The surface potential of the purple membrane was measured by a novel method by using an artificial bacteriorhodopsin whose chromophore was 13‐CF 3 retinal instead of retinal. When attached to the apoprotein by a Schiff base, the intrinsic p K of the 13‐CF 3 chromophore is around 7.3. The apparent p K of this pigment depends on the surface potential and thus on the electrolyte concentration. This allowed us to determine the surface charge density using the Gouy‐Chapman equation. The surface charge density was found to be −1.65 ± 0.15 × 10 −3 electronic charges per Å 2 or about 2 negative charges/bacteriorhodopsin. This large value for the surface potential probably explains both part of the strong apparent association of divalent cations with the membrane and the effect of low salt concentrations on light‐induced proton release from the purple membrane.