Temperature-dependent conformational changes in the bacteriopheophytins of Rhodobacter sphaeroides reaction centers

Peloquin, John M.; Violette, Carol A.; Frank, Harry A.; Bocian, David F.

doi:10.1021/bi00472a020

Cited by 16 publications

(35 citation statements)

References 43 publications

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“…For H M the scattering is weak, and no distinct peaks are observed. However, H L shows a pair of bands whose frequencies are 1661 and 1674 cm −1 at 273 K. These are assigned to the CO stretches of the acetyl group on ring I and stretches of the keto group on the isocyclic ring V, which is consistent with previous studies 3, 7b, 8a. When the temperature is lowered to 100 K the keto band is unaffected but the acetyl band disappears, and a new shoulder can be seen at 1642 cm −1 .…”

Section: Discussionsupporting

confidence: 92%

“…This result was also reported by Ivancich et al5f There are other pronounced intensity disparities between corresponding bands of H L and H M , establishing that the two spectra are distinct. We note that a similar experiment was reported in an early study by Peloquin and coworkers,7a but the spectral resolution was not high enough at that time to gauge the degree of selectivity in enhancing H L versus H M .…”

Section: Resultsmentioning

confidence: 59%

“…2) and provide opportunities for selective excitation of the chromophores. Emphasis has therefore shifted to RR spectroscopy with red‐ or near‐IR excitation 5–7. These studies are technically demanding because of the relative weakness of the Q bands and because fluorescence becomes a serious interference in this wavelength region, especially from impurities that accumulate with time and with sample handling.…”

Section: Introductionmentioning

confidence: 99%

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Selective enhancement of resonance Raman spectra of separate bacteriopheophytins inRb. sphaeroides reaction centers

et al. 2000

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Tunable dye laser excitation of carefully prepared samples of Rb. sphaeroides reaction centers provides richly detailed resonance Raman (RR) spectra of the bacteriopheophytins, H, and the accessory bacteriochlorophylls, B. These spectra demonstrate selective enhancement of the separate bacteriopheophytins on the active (HL) and inactive (HM) sides of the reaction centers. The spectra are assigned with the aid of normal coordinate analyses using force fields previously developed for porphyrins and reduced porphyrins. Comparison of the HL and HM vibrational mode frequencies reveals evidence for greater polarization of the acetyl substituent in HL than HM. This polarization is expected to make HL easier to reduce, thereby contributing to the directionality of electron transfer from the special pair, P. In addition, the acetyl polarization of HL is increased at low temperature (100 K), helping to account for the increase in electron transfer rate. The polarizing field is suggested to arise from the Mg2+ of the neighboring accessory bacteriochlorophyll, which is 4.9 Å from the acetyl O atom. The 100 K spectra show sharpening and intensification of a number of RR bands, suggesting a narrowing of the conformational distribution of chromophores, which is consistent with the reported narrowing of the distribution in electron transfer rates. Excitation at 800 nm produces high‐quality RR spectra of the accessory bacteriochlorophylls, and the spectral pattern is unaltered on tuning the excitation to 810 nm in resonance with the upper exciton transition of P. Either the resonance enhancement of P is weak, or the bacteriochlorophyll RR spectra are indistinguishable for P and B. © 2000 John Wiley & Sons, Inc. Biopolymers (Biospectroscopy) 57: 64–76, 2000

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Section: Discussionsupporting

confidence: 92%

Section: Resultsmentioning

confidence: 59%

Section: Introductionmentioning

confidence: 99%

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Selective enhancement of resonance Raman spectra of separate bacteriopheophytins inRb. sphaeroides reaction centers

et al. 2000

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“…In C. aurantiacus, where the analogous residue is glutamine, the mean time constants for both reactions (8 and 320 ps) are also both longer than in wild-type RCs from other organisms (21,22). Recent resonance Raman measurements have indicated that the BphL-GluLl" hydrogen-bonding interaction and the planarity of the BPhL macrocycle may be temperature dependent (29), providing a potential connection with the temperature dependence of the distribution of rates. Molecular factors involving P may provide additional variables giving rise to the detailed differences between the patterns in Ti and T2 discussed above.…”

Section: Methodsmentioning

confidence: 99%

Evidence that a distribution of bacterial reaction centers underlies the temperature and detection-wavelength dependence of the rates of the primary electron-transfer reactions.

Kirmaier

Holten

1990

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

194

113

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The rates of the primary electron-transfer processes in Rhodobacter sphaeroides reaction centers have been examined in detail by using 150-fs excitation flashes at 870 nm. At room temperature the apparent time constants for both initial charge separation (P* -> P+BPhj) and subsequent electron transfer (P+BPhj -+ P+QA) are found to encompass a range of values ('1.3-4 ps and "100-320 ps, respectively), depending on the wavelength at which the kinetics are followed.We suggest this reflects a distribution of reaction centers (or a few conformers), having differences in factors such as distances or orientations between the cofactors, hydrogen bonding, or other pigment-protein interactions. We also suggest that the time constants observed at cryogenic temperatures (""1.3 and "100 ps, respectively, with much smaller or negble variation with detection wavelength) do not reflect an actual increase in the rates with decreasing temperature but rather derive from a shift in the distribution of reaction centers toward those in which electron transfer inherently occurs with the faster rates.The temperature dependence of the rates of electron transfer in bacterial reaction centers (RCs) has received considerable experimental and theoretical attention. For the most part the temperature dependence of the initial charge separation step (observed to occur in ""3 ps at 295 K and 1 ps at 10 K) has been followed via the decay of the broad stimulated emission band of P*, which has a maximum near 920 nm in Rhodobacter sphaeroides (6, 7). The temperature dependence of electron transfer from BPhj to QA in Rb.sphaeroides (r 200 ps at 295 K and 100 ps at 77 K and below) similarly has been followed primarily in a single region, namely via decay of the broad BPhL anion band centered near 665 nm (5). Kinetics also have been measured at a few wavelengths near 800 nm in the recent studies of the P*-P+BPh-process, with the primary focus being a search for evidence for the possible transient reduction of the monomeric pigment BChlL (6,7,11,12). During the course of our previous investigations of electron transfer from BPhjL to QA, we examined the near-infrared (730-830 nm) region also, with the expectation of finding time constants that agreed with those measured via decay of the BPhL anion band. This proved not to be uniformly the case, however. At room temperature, for example, we found that at certain wavelengths the observed time constant was somewhat less than 200 ps, and at other wavelengths it was somewhat greater than 200 ps (5). A major limitation of these measurements was that the signal-to-noise ratio prevented a complete study in the near-infrared region in that accurate time constants at room temperature could be measured only within two narrow (-5 nm) wavelength regions centered near the peak ground state absorptions of the BPhs and the monomeric BChls.We have reexamined these findings by using instrumentation that gives a significantly better signal-to-noise ratio in AA and, in addition, utilizes 150-fs flashes (compared to...

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“…66 Resonance Raman and other vibrational techniques have been used to investigate this situation and have provided supporting information for structural flexibility of the chromophores. 67,68,69,70 This has been reviewed before 35 and an update will be given elsewhere. 71 RR spectral changes have been observed in PSI after exposure to high light intensities, indicating the extent of photodamage to the Chl a pigments and providing insight into the mechanisms of photoprotection.…”

Section: Chlorophyll Complexes In Photosynthesismentioning

confidence: 99%

61 The Structural Chemistry of Isolated Chlorophylls

Senge¹,

MacGowan²

2011

Handbook of Porphyrin Science

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Temperature-dependent conformational changes in the bacteriopheophytins of Rhodobacter sphaeroides reaction centers

Cited by 16 publications

References 43 publications

Selective enhancement of resonance Raman spectra of separate bacteriopheophytins inRb. sphaeroides reaction centers

Selective enhancement of resonance Raman spectra of separate bacteriopheophytins inRb. sphaeroides reaction centers

Evidence that a distribution of bacterial reaction centers underlies the temperature and detection-wavelength dependence of the rates of the primary electron-transfer reactions.

61 The Structural Chemistry of Isolated Chlorophylls

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