Effects of pH and acetylation on Hg(2+)-induced purple to blue transition in bacteriorhodopsin.
Effects of Hg(2+) ions on the absorption spectrum of bacteriorhodopsin have been measured at different pH values and after acetylation. UV-difference spectroscopy and CD spectra show that Hg(2+)-induced color change is essentially similar to that caused by removal of cations or acidification. The ability of Hg(2+)-induced purple-to-blue transition is pH-dependent and exhibits a maximum at pH 5.5. Acetylation influences the absorption in the same way as Hg(2+) ions and accelerates Hg(2+)-induced purple to blue transition. All these results strongly suggest that the Hg(2+) effect is not a specific binding but just a replacement of intrinsic cations on the membrane surface, where they form a double layer. The composition of the double layer determines the surface pH on the membrane, which affects the color of the bacteriorhodopsin.
Wang
G
G
Institute of Biophysics, Academia Sinica, 15 Datun Road, 100101, Beijing, China.
Hu
K S
KS
D000107:Acetylation; D001436:Bacteriorhodopsins / Q000737:chemistry* / Q000187:drug effects*; D002412:Cations / Q000737:chemistry; D002942:Circular Dichroism; D006863:Hydrogen-Ion Concentration; D008628:Mercury / Q000494:pharmacology*; D013057:Spectrum Analysis
D002412:Cations; D001436:Bacteriorhodopsins; D008628:Mercury