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Biochemistry. 1997 Jul 22;36(29):8671-6.

Glutamate-194 to cysteine mutation inhibits fast light-induced proton release in bacteriorhodopsin.

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  • 1Center for Biophysics and Computational Biology, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA.


Substitution of glutamic acid-194, a residue on the extracellular surface of bacteriorhodopsin, with a cysteine inhibits the fast light-induced proton release that normally is coupled with the deprotonation of the Schiff base during the L to M transition. Proton release in this mutant occurs at the very end of the photocycle and coincides with deprotonation of the primary proton acceptor, Asp-85, during the O to bR transition. the E194C mutation also results in a slowing down of the photocycle by about 1 order of magnitude as compared to the wild type and produces a strong effect on the pH dependence of dark adaptation that is interpreted as a drastic reduction or elimination of the coupling between the primary proton acceptor Asp-85 and the proton release group. These data indicate that Glu-194 is a critical component of the proton release complex in bacteriorhodopsin.

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