Evidence for the involvement of more than one metal cation in the Schiff base deprotonation process during the photocycle of bacteriorhodopsin

The removal of metal cations inhibits the deprotonation process of the protonated Schiff base during the photocycle of bacteriorhodopsin. To understand the nature of the involvement of these cations, a spectroscopic and kinetic study was carried out on bacteriorhodopsin samples in which the native C...

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Main Authors: Corcoran, Timothy C., Ismail, Kamal Z., El-Sayed, Mostafa A.
Formato: Artigo
Idioma:en
Publicado em: 1987
Assuntos:
Biological Sciences: Biophysics
Acesso em linha:https://ncbi.nlm.nih.gov/pmc/articles/PMC305029/
https://ncbi.nlm.nih.gov/pubmed/16593849
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spelling pubmed-3050292004-02-02 Evidence for the involvement of more than one metal cation in the Schiff base deprotonation process during the photocycle of bacteriorhodopsin Corcoran, Timothy C. Ismail, Kamal Z. El-Sayed, Mostafa A. Proc Natl Acad Sci U S A Biological Sciences: Biophysics The removal of metal cations inhibits the deprotonation process of the protonated Schiff base during the photocycle of bacteriorhodopsin. To understand the nature of the involvement of these cations, a spectroscopic and kinetic study was carried out on bacteriorhodopsin samples in which the native Ca(2+) and Mg(2+) were replaced by Eu(3+), a luminescent cation. The decay of Eu(3+) emission in bacteriorhodopsin can be fitted to a minimum of three decay components, which are assigned to Eu(3+) emission from three different sites. This is supported by the response of the decay components to the presence of (2)H(2)O and to the changes in the Eu(3+)/bR molar ratio. The number of water molecules coordinated to Eu(3+) in each site is determined from the change in its emission lifetime when (2)H(2)O replaces H(2)O. Most of the emission originates from two “wet” sites of low crystal-field symmetry—e.g., surface sites. Protonated Schiff base deprotonation has no discernable effect on the emission decay of protein-bound Eu(3+), suggesting an indirect involvement of metal cations in the deprotonation process. Adding Eu(3+) to deionized bacteriorhodopsin increases the emission intensity of each Eu(3+) site linearly, but the extent of the deprotonation (and color) changes sigmoidally. This suggests that if only the emitting Eu(3+) ions cause the deprotonation and bacteriorhodopsin color change, ions in more than one site must be involved—e.g., by inducing protein conformation changes. The latter could allow deprotonation by the interaction between the protonated Schiff base and a positive field of cations either on the surface or within the protein. 1987-06 /pmc/articles/PMC305029/ /pubmed/16593849 Text en
institution US National Library of Medicine
collection PubMed Central
language en
format Article
topic Biological Sciences: Biophysics
spellingShingle Biological Sciences: Biophysics
Corcoran, Timothy C.
Ismail, Kamal Z.
El-Sayed, Mostafa A.
Evidence for the involvement of more than one metal cation in the Schiff base deprotonation process during the photocycle of bacteriorhodopsin
description The removal of metal cations inhibits the deprotonation process of the protonated Schiff base during the photocycle of bacteriorhodopsin. To understand the nature of the involvement of these cations, a spectroscopic and kinetic study was carried out on bacteriorhodopsin samples in which the native Ca(2+) and Mg(2+) were replaced by Eu(3+), a luminescent cation. The decay of Eu(3+) emission in bacteriorhodopsin can be fitted to a minimum of three decay components, which are assigned to Eu(3+) emission from three different sites. This is supported by the response of the decay components to the presence of (2)H(2)O and to the changes in the Eu(3+)/bR molar ratio. The number of water molecules coordinated to Eu(3+) in each site is determined from the change in its emission lifetime when (2)H(2)O replaces H(2)O. Most of the emission originates from two “wet” sites of low crystal-field symmetry—e.g., surface sites. Protonated Schiff base deprotonation has no discernable effect on the emission decay of protein-bound Eu(3+), suggesting an indirect involvement of metal cations in the deprotonation process. Adding Eu(3+) to deionized bacteriorhodopsin increases the emission intensity of each Eu(3+) site linearly, but the extent of the deprotonation (and color) changes sigmoidally. This suggests that if only the emitting Eu(3+) ions cause the deprotonation and bacteriorhodopsin color change, ions in more than one site must be involved—e.g., by inducing protein conformation changes. The latter could allow deprotonation by the interaction between the protonated Schiff base and a positive field of cations either on the surface or within the protein.
author Corcoran, Timothy C.
Ismail, Kamal Z.
El-Sayed, Mostafa A.
author_facet Corcoran, Timothy C.
Ismail, Kamal Z.
El-Sayed, Mostafa A.
author_sort Corcoran, Timothy C.
title Evidence for the involvement of more than one metal cation in the Schiff base deprotonation process during the photocycle of bacteriorhodopsin
title_short Evidence for the involvement of more than one metal cation in the Schiff base deprotonation process during the photocycle of bacteriorhodopsin
title_full Evidence for the involvement of more than one metal cation in the Schiff base deprotonation process during the photocycle of bacteriorhodopsin
title_fullStr Evidence for the involvement of more than one metal cation in the Schiff base deprotonation process during the photocycle of bacteriorhodopsin
title_full_unstemmed Evidence for the involvement of more than one metal cation in the Schiff base deprotonation process during the photocycle of bacteriorhodopsin
title_sort evidence for the involvement of more than one metal cation in the schiff base deprotonation process during the photocycle of bacteriorhodopsin
publishDate 1987
url https://ncbi.nlm.nih.gov/pmc/articles/PMC305029/
https://ncbi.nlm.nih.gov/pubmed/16593849
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