Manipulating the direction of electron transfer in the bacterial reaction center by swapping phe for Tyr near BChlM (L181) and Tyr for phe near BChlL (M208)

C. Kirmaier, C. He, D. Holten

Research output: Contribution to journalArticle

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Abstract

We have investigated the primary charge separation processes in Rb. capsulatus reaction centers (RCs) bearing the mutations Phe(L181) → Tyr, Tyr(M208) → Phe, and Leu(M212) → His. In the YFH mutant, decay of the excited primary electron donor P* occurs with an 11±2 ps time constant and is trifurcated to give (1) internal conversion to the ground state (∼10% yield), (2) charge separation to the L side of the RC (∼60% yield), and (3) electron transfer to the M-side bacteriopheophytin BPhM (∼30% yield). These results relate previous work in which the ionizable residues Lys (at L178) and Asp (at M201) have been used to facilitate charge separation to the M side of the RC, and the widely studied L181 and M208 mutants. One conclusion that comes from this work is that the Tyr (M208) → Pre and Gly(M201) → Asp mutations near the L-side bacteriochlorophyll (BChlL) raise the free energy of P+BChlL- by comparable amounts. The results also suggest that the free energy of P+BChlM- is lowered more substantially by a Tyr at L181 than a Lys at L178. The results on the YFH mutant further demonstrate that the free energy differences between the L- and M-side charge-separated states play a significant role in the directionality of charge separation in the wild-type RC, and place limits on the contributing role of differential electronic matrix elements on the two sides of the RC.

Original languageEnglish (US)
Pages (from-to)12132-12139
Number of pages8
JournalBiochemistry
Volume40
Issue number40
DOIs
StatePublished - Oct 9 2001
Externally publishedYes

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Bacteriochlorophylls
Electrons
Free energy
Mutation
Viperidae
Bearings (structural)
Ground state
Direction compound
bacteriopheophytin

ASJC Scopus subject areas

  • Biochemistry

Cite this

Manipulating the direction of electron transfer in the bacterial reaction center by swapping phe for Tyr near BChlM (L181) and Tyr for phe near BChlL (M208). / Kirmaier, C.; He, C.; Holten, D.

In: Biochemistry, Vol. 40, No. 40, 09.10.2001, p. 12132-12139.

Research output: Contribution to journalArticle

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abstract = "We have investigated the primary charge separation processes in Rb. capsulatus reaction centers (RCs) bearing the mutations Phe(L181) → Tyr, Tyr(M208) → Phe, and Leu(M212) → His. In the YFH mutant, decay of the excited primary electron donor P* occurs with an 11±2 ps time constant and is trifurcated to give (1) internal conversion to the ground state (∼10{\%} yield), (2) charge separation to the L side of the RC (∼60{\%} yield), and (3) electron transfer to the M-side bacteriopheophytin BPhM (∼30{\%} yield). These results relate previous work in which the ionizable residues Lys (at L178) and Asp (at M201) have been used to facilitate charge separation to the M side of the RC, and the widely studied L181 and M208 mutants. One conclusion that comes from this work is that the Tyr (M208) → Pre and Gly(M201) → Asp mutations near the L-side bacteriochlorophyll (BChlL) raise the free energy of P+BChlL- by comparable amounts. The results also suggest that the free energy of P+BChlM- is lowered more substantially by a Tyr at L181 than a Lys at L178. The results on the YFH mutant further demonstrate that the free energy differences between the L- and M-side charge-separated states play a significant role in the directionality of charge separation in the wild-type RC, and place limits on the contributing role of differential electronic matrix elements on the two sides of the RC.",
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AU - He, C.

AU - Holten, D.

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N2 - We have investigated the primary charge separation processes in Rb. capsulatus reaction centers (RCs) bearing the mutations Phe(L181) → Tyr, Tyr(M208) → Phe, and Leu(M212) → His. In the YFH mutant, decay of the excited primary electron donor P* occurs with an 11±2 ps time constant and is trifurcated to give (1) internal conversion to the ground state (∼10% yield), (2) charge separation to the L side of the RC (∼60% yield), and (3) electron transfer to the M-side bacteriopheophytin BPhM (∼30% yield). These results relate previous work in which the ionizable residues Lys (at L178) and Asp (at M201) have been used to facilitate charge separation to the M side of the RC, and the widely studied L181 and M208 mutants. One conclusion that comes from this work is that the Tyr (M208) → Pre and Gly(M201) → Asp mutations near the L-side bacteriochlorophyll (BChlL) raise the free energy of P+BChlL- by comparable amounts. The results also suggest that the free energy of P+BChlM- is lowered more substantially by a Tyr at L181 than a Lys at L178. The results on the YFH mutant further demonstrate that the free energy differences between the L- and M-side charge-separated states play a significant role in the directionality of charge separation in the wild-type RC, and place limits on the contributing role of differential electronic matrix elements on the two sides of the RC.

AB - We have investigated the primary charge separation processes in Rb. capsulatus reaction centers (RCs) bearing the mutations Phe(L181) → Tyr, Tyr(M208) → Phe, and Leu(M212) → His. In the YFH mutant, decay of the excited primary electron donor P* occurs with an 11±2 ps time constant and is trifurcated to give (1) internal conversion to the ground state (∼10% yield), (2) charge separation to the L side of the RC (∼60% yield), and (3) electron transfer to the M-side bacteriopheophytin BPhM (∼30% yield). These results relate previous work in which the ionizable residues Lys (at L178) and Asp (at M201) have been used to facilitate charge separation to the M side of the RC, and the widely studied L181 and M208 mutants. One conclusion that comes from this work is that the Tyr (M208) → Pre and Gly(M201) → Asp mutations near the L-side bacteriochlorophyll (BChlL) raise the free energy of P+BChlL- by comparable amounts. The results also suggest that the free energy of P+BChlM- is lowered more substantially by a Tyr at L181 than a Lys at L178. The results on the YFH mutant further demonstrate that the free energy differences between the L- and M-side charge-separated states play a significant role in the directionality of charge separation in the wild-type RC, and place limits on the contributing role of differential electronic matrix elements on the two sides of the RC.

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