Computer analysis of spectra with strongly overlapping lines. Application to TRIPLE resonance spectra of the chlorophyll a cation radical

Tränkle, E.; Lendzian, Friedhelm

doi:10.1016/0022-2364(89)90118-2

Cited by 11 publications

(16 citation statements)

References 12 publications

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“…Therefore, this technique can be also be used to assign lines in a spectrum to different species of RCs. For the evaluation of spectra with overlapping lines a spectral deconvolution program was employed (Trankle & Lendzian, 1989).…”

Section: Methodsmentioning

confidence: 99%

ENDOR Studies of the Primary Donor Cation Radical in Mutant Reaction Centers of Rhodobacter sphaeroides with Altered Hydrogen-Bond Interactions

et al. 1995

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The electronic structure of the cation radical of the primary electron donor was investigated in genetically modified reaction centers of Rhodobacter sphaeroides. The site-directed mutations were designed to add or remove hydrogen bonds between the conjugated carbonyl groups of the primary donor, a bacteriochlorophyll dimer, and histidine residues of the protein and were introduced at the symmetry-related sites L168 His-->Phe, HF(L168), and M197 Phe-->His, FH(M197), near the 2-acetyl groups of the dimer and at sites M160 Leu-->His, LH(M160), and L131 Leu-->His, LH(L131), in the vicinity of the 9-keto carbonyls of the dimer. The single mutants and a complete set of double mutants were studied using EPR, ENDOR, and TRIPLE resonance spectroscopy. The changes in the hydrogen bond situation of the primary donor were accompanied by changes in the dimer oxidation midpoint potential, ranging from 410 to 710 mV in the investigated mutants [Lin, X., Murchison, H. A., Nagarajan, V., Parson, W. W., Williams, J. C. & Allen, J. P. (1994) Proc. Natl. Acad. Sci. U.S.A. 91, 10265-10269]. It was found that the addition or removal of a hydrogen bond causes large shifts of the spin density between the two halves of the dimer. Measurements on double mutants showed that the unpaired electron can be gradually shifted from a localization on the L-half of the dimer to a localization on the M-half, depending on the hydrogen bond situation. As a control, the effects of the different hydrogen bonds on P.+ in the mutant HL(M202), which contains a BChlL-BPheM heterodimer as the primary donor with localized spin on the BChl aL [Bylina, E. J., & Youvan, D. C. (1988) Proc. Natl. Acad. Sci. U.S.A. 85, 7226-7230; Schenck, C. C., Gaul, D., Steffen M., Boxer S. G., McDowell L., Kirmaier C., & Holten D. (1990) in Reaction Centers of Photosynthetic Bacteria (Michel-Beyerle M. E., Ed.) pp 229-238, Springer, Berlin] were studied. In this mutant only small local changes of the spin densities (< or = 10%) in the vicinity of the hydrogen bonds were observed. The effects of the introduced hydrogen bonds on the spin density distribution of the dimer in the mutants are discussed in terms of different orbital energies of the two BChl a moieties which are directly influenced by hydrogen bond formation. The observed changes of the spin density distribution for the double mutants are additive with respect to the single mutations.(ABSTRACT TRUNCATED AT 400 WORDS)

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Section: Methodsmentioning

confidence: 99%

ENDOR Studies of the Primary Donor Cation Radical in Mutant Reaction Centers of Rhodobacter sphaeroides with Altered Hydrogen-Bond Interactions

et al. 1995

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“…The cation radical of the BChl dimer was generated in the cavity by continuous wave illumination with a tungsten halogen lamp (100 W, 700-950 nm using filters) (23). The hfcs were determined by fits of the spectra (25), and the spin density distribution was calculated from the ratios of the methyl hfcs assigned to each half of the dimer as described below.…”

Section: Methodsmentioning

confidence: 99%

Relationship between the oxidation potential and electron spin density of the primary electron donor in reaction centers from Rhodobacter sphaeroides

Artz

Williams

Allen

et al. 1997

Proc. Natl. Acad. Sci. U.S.A.

124

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The primary electron donor in bacterial reaction centers is a dimer of bacteriochlorophyll a molecules, labeled L or M based on their proximity to the symmetryrelated protein subunits. The electronic structure of the bacteriochlorophyll dimer was probed by introducing small systematic variations in the bacteriochlorophyll-protein interactions by a series of site-directed mutations that replaced residue Leu M160 with histidine, tyrosine, glutamic acid, glutamine, aspartic acid, asparagine, lysine, and serine. The midpoint potentials for oxidation of the dimer in the mutants showed an almost continuous increase up to Ϸ60 mV compared with wild type. The spin density distribution of the unpaired electron in the cation radical state of the dimer was determined by electron-nuclear-nuclear triple resonance spectroscopy in solution. The ratio of the spin density on the L side of the dimer to the M side varied from Ϸ2:1 to Ϸ5:1 in the mutants compared with Ϸ2:1 for wild type. The correlation between the midpoint potential and spin density distribution was described using a simple molecular orbital model, in which the major effect of the mutations is assumed to be a change in the energy of the M half of the dimer, providing estimates for the coupling and energy levels of the orbitals in the dimer. These results demonstrate that the midpoint potential can be fine-tuned by electrostatic interactions with amino acids near the dimer and show that the properties of the electronic structure of a donor or acceptor in a protein complex can be directly related to functional properties such as the oxidation-reduction midpoint potential.The reaction center is the site of the primary process in photosynthesis, which is the conversion of light energy into a charge-separated state (for reviews, see ref. 1). The electron transfer process in the reaction center has the remarkable aspect that the quantum yield is near unity, that is, for every photon absorbed, one electron is transferred. The reaction center isolated from the purple bacterium Rhodobacter sphaeroides is particularly useful for the study of electron transfer because this complex has been well characterized biochemically and spectroscopically, and the three-dimensional structure has been determined by x-ray diffraction (2-5). The reaction center has two core subunits, L and M, that form the binding sites for the cofactors and are related by an Ϸ2-fold symmetry axis. The primary electron donor (P) consists of two symmetry-related bacteriochlorophyll (BChl) a molecules labeled P L and P M that overlap at the ring I position and are separated by Ϸ3.5 Å (Fig. 1). Light absorption causes the excitation of P, and within 3.5 ps, an electron is transferred to a bacteriopheophytin acceptor. Electron transfer proceeds to the primary quinone acceptor, Q A , in Ϸ200 ps and to the secondary quinone, Q B , in Ϸ200 s. After reduction of the donor by cytochrome c 2 , absorption of a second photon leads to the transfer of a second electron to Q B , which then leaves the protein carry...

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“…Deconvolution of the ENDOR spectra was achieved with the program Compass. 43 The A zz values are collected in Table 1.…”

Section: Resultsmentioning

confidence: 99%

“…PTC as derived from the time-resolved ENDOR experiments shown in Fig.5. The magnitudes were determined by deconvolution of the ENDOR spectra by the program Compass,43 and the signs as set out in the text. The dipolar 'matrix' couplings are not A zz hyperfine coupling tensor components and so are given the label x in the table (experimental error ±0.1 MHz).…”

mentioning

confidence: 99%

Time-resolved EPR and ENDOR study of the photoexcited triplet state of free-base tetraphenylchlorin in a crystalline toluene matrix †

Kay¹,

Valentin²,

Möbius³

1997

J. Chem. Soc., Perkin Trans. 2

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A time-resolved EPR and ENDOR study of the photoexcited triplet state of the free-base tetraphenylchlorin has been made in a polycrystalline toluene matrix at 120 K. Crystallization of the toluene results in a partially aligned sample. The nature of the orientation of the solute molecules is investigated by timeresolved EPR spectroscopy using the anisotropy of the zero-field splitting tensor of the triplet state as the observable parameter. It is determined that 55% of the triplet molecules are oriented in a single crystal-like domain with the triplet z-axes oriented within 15Њ of the magnetic field. In the ENDOR study selective excitation, of only those molecules which have their triplet z-axes parallel to the magnetic field, has permitted the measurement of the A zz component of the hyperfine coupling tensor of protons, in the reference frame of the zero-field splitting tensor. The sign and magnitude of the matrix couplings are also determined. The use of the partially oriented sample drastically enhanced the signal intensity over that achieved in a randomly oriented sample by increasing the number of molecules with their triplet z-axes parallel to the magnetic field. Additionally, time-resolved ENDOR spectroscopy allowed the hyperfine interactions to be determined at far higher temperatures than usual for the study of triplet states.

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Computer analysis of spectra with strongly overlapping lines. Application to TRIPLE resonance spectra of the chlorophyll a cation radical

Cited by 11 publications

References 12 publications

ENDOR Studies of the Primary Donor Cation Radical in Mutant Reaction Centers of Rhodobacter sphaeroides with Altered Hydrogen-Bond Interactions

ENDOR Studies of the Primary Donor Cation Radical in Mutant Reaction Centers of Rhodobacter sphaeroides with Altered Hydrogen-Bond Interactions

Relationship between the oxidation potential and electron spin density of the primary electron donor in reaction centers from Rhodobacter sphaeroides

Time-resolved EPR and ENDOR study of the photoexcited triplet state of free-base tetraphenylchlorin in a crystalline toluene matrix †

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