Manipulations of the B-Side Charge-Separated States' Energetics in the Rhodobacter sphaeroides Reaction Center

Evaldas Katilius, Jennie Bever, Zivile Katiliene, Su Lin, Aileen K W Taguchi, Neal Woodbury

Research output: Contribution to journalArticle

16 Citations (Scopus)

Abstract

The mutation HL(M182) in the Rb. sphaeroides reaction center (RC) results in the replacement of the monomer bacteriochlorophyll on the inactive side (B side) of the reaction center with a bacteriopheophytin (φB). In φB containing reaction centers, excitation of the initial electron donor, the special pair P, results in about 35% electron transfer along the normally inactive B side. However, the electron is transferred only to the exchanged cofactor φB. Several additional mutations in close proximity to bacteriopheophytins φB or HB have been created with the goal of altering the energetics of charge-separated states P+φB - and P+H B -. Aspartic acid residues were introduced to replace methionine L174 or valine M175 in the vicinity of the φB cofactor in order to raise the free energy of state P-φ B -. Threonine M133 was mutated to the aspartic acid to add a hydrogen bond to the HB cofactor and lower the free energy of state P+HB -. The mutations in the environment surrounding the φB pigment resulted in a decrease in the quantum yield of P+φB - as well as a decrease in the recombination lifetime of this state. The mutation of valine M175 to aspartic acid showed the largest effect. The yield of state P +φB - decreased to about 25% and its recombination lifetime shortened from 200 to 125 ps. This additional mutation also resulted in the loss of the carotenoid molecule from the reaction centers. None of the three additional mutations altered the free energies sufficiently to result in observable electron transfer to HB. However, these measurements have allowed a more accurate assignment of the B-side charge-separated states' energetics than was previously possible.

Original languageEnglish (US)
Pages (from-to)12029-12034
Number of pages6
JournalJournal of Physical Chemistry B
Volume107
Issue number43
StatePublished - Oct 30 2003

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mutations
manipulators
Aspartic Acid
Free energy
aspartic acid
Electrons
Valine
Acids
free energy
Bacteriochlorophylls
electron transfer
Quantum yield
Threonine
Carotenoids
Pigments
Methionine
methionine
life (durability)
carotenoids
Hydrogen bonds

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry

Cite this

Manipulations of the B-Side Charge-Separated States' Energetics in the Rhodobacter sphaeroides Reaction Center. / Katilius, Evaldas; Bever, Jennie; Katiliene, Zivile; Lin, Su; Taguchi, Aileen K W; Woodbury, Neal.

In: Journal of Physical Chemistry B, Vol. 107, No. 43, 30.10.2003, p. 12029-12034.

Research output: Contribution to journalArticle

Katilius, Evaldas ; Bever, Jennie ; Katiliene, Zivile ; Lin, Su ; Taguchi, Aileen K W ; Woodbury, Neal. / Manipulations of the B-Side Charge-Separated States' Energetics in the Rhodobacter sphaeroides Reaction Center. In: Journal of Physical Chemistry B. 2003 ; Vol. 107, No. 43. pp. 12029-12034.
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abstract = "The mutation HL(M182) in the Rb. sphaeroides reaction center (RC) results in the replacement of the monomer bacteriochlorophyll on the inactive side (B side) of the reaction center with a bacteriopheophytin (φB). In φB containing reaction centers, excitation of the initial electron donor, the special pair P, results in about 35{\%} electron transfer along the normally inactive B side. However, the electron is transferred only to the exchanged cofactor φB. Several additional mutations in close proximity to bacteriopheophytins φB or HB have been created with the goal of altering the energetics of charge-separated states P+φB - and P+H B -. Aspartic acid residues were introduced to replace methionine L174 or valine M175 in the vicinity of the φB cofactor in order to raise the free energy of state P-φ B -. Threonine M133 was mutated to the aspartic acid to add a hydrogen bond to the HB cofactor and lower the free energy of state P+HB -. The mutations in the environment surrounding the φB pigment resulted in a decrease in the quantum yield of P+φB - as well as a decrease in the recombination lifetime of this state. The mutation of valine M175 to aspartic acid showed the largest effect. The yield of state P +φB - decreased to about 25{\%} and its recombination lifetime shortened from 200 to 125 ps. This additional mutation also resulted in the loss of the carotenoid molecule from the reaction centers. None of the three additional mutations altered the free energies sufficiently to result in observable electron transfer to HB. However, these measurements have allowed a more accurate assignment of the B-side charge-separated states' energetics than was previously possible.",
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