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Title: Pathway of proton transfer in bacterial reaction centers: Replacement of serine-L223 by alanine inhibits electron and proton transfers associated with reduction of quinone to dihydroquinone

Abstract

The pathway of proton transfer in the reaction center (RC) from Rhodobacter sphaeroides was investigated by site-directed mutagenesis. Ser-L223, a putative proton donor that forms a hydrogen bond with the secondary quinone acceptor Q{sub B}, was replaced with Ala and Thr. RCs with Ala-L223 displayed reduced electron transfer and proton uptake rates in the reaction Q{sub A}{sup {minus}}Q{sub B}{sup {minus}} + 2H{sup +} {yields} Q{sub A}Q{sub B}H{sub 2}. The rate constant for this reaction, k{sub AB}{sup (2)}, was found to be reduced {approx}350-fold to 4.0 {plus minus} 0.2 s{sup {minus}1}. Prton uptake measurements using a pH indicator dye showed a rapid uptake of 1 H{sup +} per RC followed by a slower uptake of 1 H{sup +} per RC at a rate of 4.1 {plus minus} 0.1 s{sup {minus}1}; native RCs showed a rapid uptake of 2H{sup +} per RC. Evidence is provided that these changes were not due to gross structural changes in the binding site of Q{sub B}. RCs with Thr-L223 showed little reduction in the rats of electron and proton transfer. These results indicate that proton transfer from the hydroxyl group of Ser-L223 or Thr-L223 is required for fast electron and proton transfer associated with the formationmore » of the dihydroquinone QH{sub 2}. In contrast, previous work showed that replacing Glu-L212, another putative proton donor to Q{sub B}, with Gln slowed proton uptake from solution without significantly altering electron transfer. The authors propose a model that involves two distinct proton transfer steps. The first step occurs prior to transfer of the second electron to Q{sub B} and involves proton transfer from Ser-L223. The second step occurs after this electron transfer through a pathway involving Glu-L212.« less

Authors:
; ; ;  [1]
  1. Univ. of California, San Diego, La Jolla (USA)
Publication Date:
OSTI Identifier:
5489388
Resource Type:
Journal Article
Journal Name:
Proceedings of the National Academy of Sciences of the United States of America; (United States)
Additional Journal Information:
Journal Volume: 87:17; Journal ID: ISSN 0027-8424
Country of Publication:
United States
Language:
English
Subject:
14 SOLAR ENERGY; PHOTOSYNTHETIC REACTION CENTERS; BIOLOGICAL PATHWAYS; QUINONES; REDUCTION; ALANINES; CYTOCHROMES; ELECTRON SPIN RESONANCE; ELECTRON TRANSFER; HYDROGEN TRANSFER; PHOTOSYNTHETIC BACTERIA; PROTONS; SERINE; STOICHIOMETRY; AMINO ACIDS; AROMATICS; BARYONS; CARBOXYLIC ACIDS; CHEMICAL REACTIONS; ELEMENTARY PARTICLES; FERMIONS; HADRONS; HYDROXY ACIDS; MAGNETIC RESONANCE; NUCLEONS; ORGANIC ACIDS; ORGANIC COMPOUNDS; ORGANIC OXYGEN COMPOUNDS; PIGMENTS; PROTEINS; RESONANCE; 140505* - Solar Energy Conversion- Photochemical, Photobiological, & Thermochemical Conversion- (1980-)

Citation Formats

Paddock, M L, McPherson, P H, Feher, G, and Okamura, M Y. Pathway of proton transfer in bacterial reaction centers: Replacement of serine-L223 by alanine inhibits electron and proton transfers associated with reduction of quinone to dihydroquinone. United States: N. p., 1990. Web. doi:10.1073/pnas.87.17.6803.
Paddock, M L, McPherson, P H, Feher, G, & Okamura, M Y. Pathway of proton transfer in bacterial reaction centers: Replacement of serine-L223 by alanine inhibits electron and proton transfers associated with reduction of quinone to dihydroquinone. United States. https://doi.org/10.1073/pnas.87.17.6803
Paddock, M L, McPherson, P H, Feher, G, and Okamura, M Y. 1990. "Pathway of proton transfer in bacterial reaction centers: Replacement of serine-L223 by alanine inhibits electron and proton transfers associated with reduction of quinone to dihydroquinone". United States. https://doi.org/10.1073/pnas.87.17.6803.
@article{osti_5489388,
title = {Pathway of proton transfer in bacterial reaction centers: Replacement of serine-L223 by alanine inhibits electron and proton transfers associated with reduction of quinone to dihydroquinone},
author = {Paddock, M L and McPherson, P H and Feher, G and Okamura, M Y},
abstractNote = {The pathway of proton transfer in the reaction center (RC) from Rhodobacter sphaeroides was investigated by site-directed mutagenesis. Ser-L223, a putative proton donor that forms a hydrogen bond with the secondary quinone acceptor Q{sub B}, was replaced with Ala and Thr. RCs with Ala-L223 displayed reduced electron transfer and proton uptake rates in the reaction Q{sub A}{sup {minus}}Q{sub B}{sup {minus}} + 2H{sup +} {yields} Q{sub A}Q{sub B}H{sub 2}. The rate constant for this reaction, k{sub AB}{sup (2)}, was found to be reduced {approx}350-fold to 4.0 {plus minus} 0.2 s{sup {minus}1}. Prton uptake measurements using a pH indicator dye showed a rapid uptake of 1 H{sup +} per RC followed by a slower uptake of 1 H{sup +} per RC at a rate of 4.1 {plus minus} 0.1 s{sup {minus}1}; native RCs showed a rapid uptake of 2H{sup +} per RC. Evidence is provided that these changes were not due to gross structural changes in the binding site of Q{sub B}. RCs with Thr-L223 showed little reduction in the rats of electron and proton transfer. These results indicate that proton transfer from the hydroxyl group of Ser-L223 or Thr-L223 is required for fast electron and proton transfer associated with the formation of the dihydroquinone QH{sub 2}. In contrast, previous work showed that replacing Glu-L212, another putative proton donor to Q{sub B}, with Gln slowed proton uptake from solution without significantly altering electron transfer. The authors propose a model that involves two distinct proton transfer steps. The first step occurs prior to transfer of the second electron to Q{sub B} and involves proton transfer from Ser-L223. The second step occurs after this electron transfer through a pathway involving Glu-L212.},
doi = {10.1073/pnas.87.17.6803},
url = {https://www.osti.gov/biblio/5489388}, journal = {Proceedings of the National Academy of Sciences of the United States of America; (United States)},
issn = {0027-8424},
number = ,
volume = 87:17,
place = {United States},
year = {Sat Sep 01 00:00:00 EDT 1990},
month = {Sat Sep 01 00:00:00 EDT 1990}
}