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Involvement of Histidine 190 on the D1 Protein in Electron/Proton Transfer Reactions on the Donor Side of Photosystem II

Mamedov, Fikret LU ; Sayre, Richard T and Styring, Stenbjörn LU (1998) In Biochemistry 37(40). p.14245-14256
Abstract
Flash-induced chlorophyll fluorescence kinetics from photosystem II in thylakoids from the dark-grown wild type and two site-directed mutants of the D1 protein His190 residue (D1-H190) in Chlamydomonas reinhardtii have been characterized. Induction of the chlorophyll fluorescence on the first flash, reflecting electron transport from YZ to P680+, exhibited a strong pH dependence with a pK of 7.6 in the dark-grown wild type which lacks the Mn cluster. The chlorophyll fluorescence decay, measured in the presence of DCMU, which reflects recombination between QA- and YZox, was also pH-dependent with a similar pK of 7.5. These results indicate participation by the same base, which is suggested to be D1-H190, in oxidation and reduction of YZ in... (More)
Flash-induced chlorophyll fluorescence kinetics from photosystem II in thylakoids from the dark-grown wild type and two site-directed mutants of the D1 protein His190 residue (D1-H190) in Chlamydomonas reinhardtii have been characterized. Induction of the chlorophyll fluorescence on the first flash, reflecting electron transport from YZ to P680+, exhibited a strong pH dependence with a pK of 7.6 in the dark-grown wild type which lacks the Mn cluster. The chlorophyll fluorescence decay, measured in the presence of DCMU, which reflects recombination between QA- and YZox, was also pH-dependent with a similar pK of 7.5. These results indicate participation by the same base, which is suggested to be D1-H190, in oxidation and reduction of YZ in forward electron transfer and recombination pathways, respectively. This hypothesis was tested in the D1-H190 mutants. Induction of chlorophyll fluorescence in these H190 mutants has been observed to be inefficient due to slow electron transfer from YZ to P680+ [Roffey, R. A., et al. (1994) Biochim. Biophys. Acta 1185, 257-270]. We show that this reaction is pH-dependent, with a pK of 8.1, and at pH 9, the fluorescence induction is efficient in the H190 mutants, suggesting direct titration of YZ. The efficient oxidation of YZ (70% at pH 9.0) at high pH was confirmed by kinetic EPR measurements. In contrast to the wild type, the H190 mutants show little or no observable fluorescence decay. Our data suggest that H190 is an essential component in the electron transfer reactions in photosystem II and acts as a proton acceptor upon YZ oxidation. In the H190 mutants, this reaction is inefficient and YZ oxidation only occurs at elevated pHs when YZ itself probably is deprotonated. We also propose that H190 is able to return a proton to YZox during electron recombination from QA- in a reaction which does not take place in the D1-H190 mutants. (Less)
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author
organization
publishing date
type
Contribution to journal
publication status
published
subject
in
Biochemistry
volume
37
issue
40
pages
14245 - 14256
publisher
The American Chemical Society
external identifiers
  • scopus:0032491189
ISSN
0006-2960
DOI
10.1021/bi980194j
language
English
LU publication?
yes
id
03308184-c0f1-4848-ae0c-e71da90e1fb1 (old id 125562)
date added to LUP
2007-07-06 11:08:41
date last changed
2017-10-01 03:38:28
@article{03308184-c0f1-4848-ae0c-e71da90e1fb1,
  abstract     = {Flash-induced chlorophyll fluorescence kinetics from photosystem II in thylakoids from the dark-grown wild type and two site-directed mutants of the D1 protein His190 residue (D1-H190) in Chlamydomonas reinhardtii have been characterized. Induction of the chlorophyll fluorescence on the first flash, reflecting electron transport from YZ to P680+, exhibited a strong pH dependence with a pK of 7.6 in the dark-grown wild type which lacks the Mn cluster. The chlorophyll fluorescence decay, measured in the presence of DCMU, which reflects recombination between QA- and YZox, was also pH-dependent with a similar pK of 7.5. These results indicate participation by the same base, which is suggested to be D1-H190, in oxidation and reduction of YZ in forward electron transfer and recombination pathways, respectively. This hypothesis was tested in the D1-H190 mutants. Induction of chlorophyll fluorescence in these H190 mutants has been observed to be inefficient due to slow electron transfer from YZ to P680+ [Roffey, R. A., et al. (1994) Biochim. Biophys. Acta 1185, 257-270]. We show that this reaction is pH-dependent, with a pK of 8.1, and at pH 9, the fluorescence induction is efficient in the H190 mutants, suggesting direct titration of YZ. The efficient oxidation of YZ (70% at pH 9.0) at high pH was confirmed by kinetic EPR measurements. In contrast to the wild type, the H190 mutants show little or no observable fluorescence decay. Our data suggest that H190 is an essential component in the electron transfer reactions in photosystem II and acts as a proton acceptor upon YZ oxidation. In the H190 mutants, this reaction is inefficient and YZ oxidation only occurs at elevated pHs when YZ itself probably is deprotonated. We also propose that H190 is able to return a proton to YZox during electron recombination from QA- in a reaction which does not take place in the D1-H190 mutants.},
  author       = {Mamedov, Fikret and Sayre, Richard T and Styring, Stenbjörn},
  issn         = {0006-2960},
  language     = {eng},
  number       = {40},
  pages        = {14245--14256},
  publisher    = {The American Chemical Society},
  series       = {Biochemistry},
  title        = {Involvement of Histidine 190 on the D1 Protein in Electron/Proton Transfer Reactions on the Donor Side of Photosystem II},
  url          = {http://dx.doi.org/10.1021/bi980194j},
  volume       = {37},
  year         = {1998},
}