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The use of tryptophan mutants in identifying the 296 nm transient absorbing species during the photocycle of bacteriorhodopsin

Authors
Journal
FEBS Letters
0014-5793
Publisher
Wiley Blackwell (John Wiley & Sons)
Publication Date
Volume
284
Issue
1
Identifiers
DOI: 10.1016/0014-5793(91)80749-s
Keywords
  • Bacteriorhodopsin Photocycle
  • Tyrosinate Formation
  • Tryptophan Mutant
  • Uv Transient Absorption
Disciplines
  • Chemistry

Abstract

Abstract The transient absorption at 296 nm was part of the spectroscopic evidence that initiated the proposal that tyrosinate (Tyr −) is formed during, and important to, the photocycle of bacteriorhodopsin (bR). Recent evidence against such a proposal comes from the results or NMR, UV Raman as well as electron cryo-microscopic structural studies. This makes it credible to assign this absorption to a charge perturbation of the lowest energy absorption of one of the tryptophan (Trp) residues in bR. The transient absorption at 296 nm is examined for each of 8 tryptophan mutants in which Trp is substituted by phenylalanine or cysteine, which absorb at shorter wavelength. It is shown that while all go through the photocycle, all but Trp-182 mutant show this transient absorption. This strongly suggests the assignment of this absorption to a charge perturbation of the lowest energy absorption of Trp-182 during the photocycle. The chemical identity of the perturbing charge(s) is briefly discussed.

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