A Thermal Broadening Analysis of Absorption Spectra of the D1/D2/Cytochrome b-559 Complex in Terms of Gaussian Decomposition Sub-bands

Abstract

Absorption spectra of the isolated D1/D2/cytochrome b-559 complex have been measured in the temperature range 80-300 K. All spectra were analyzed in terms of a linear combination of Gaussian bands and the thermal broadening data interpreted in terms of a model in which the spectrum of each pigment site is broadened by (a) a homogeneous component due to linear electron-phonon coupling to a low-frequency protein vibration and (b) an inhomogeneous component associated with stochastic fluctuations at each pigment site. In order to obtain a numerically adequate description of the absorption spectra, a minimum number of five sub-bands is required. Further refinement of this sub-band description was achieved by taking into account published data from hole burning and absorption difference spectroscopy. In this way, both a six sub-band description and a seven sub-band description were generated. In arriving at the seven sub-band description, the original five sub-band wavelength positions were essentially unchanged. Thermal broadening analysis of the seven sub-band description yielded data which displayed the closest correspondence with the literature observations. The wavelength positions of the sub-bands were near 661, 667, 670, and 675 nm, with two bands near 680 and 684 nm. The two almost isoenergetic sub-bands near 680 nm, identified as P680 and pheophytin, have optical reorganization energies around 40 and 16 cm-1, respectively. All other sub-bands, identified as accessory pigments, have optical reorganization energies close to 16 cm-1.(ABSTRACT TRUNCATED AT 250 WORDS)

Purification and Spectroscopic Characterization of Photosystem II Reaction Center Complexes Isolated with or without Triton X-100

“…Part of these red states have previously been ascribed to the multimer of P-680 . 4 K spectra with deep valleys have also been reported in Triton-derived preparations (van Kan et al, 1990;Chang et al, 1994a;Cattanea et al, 1995), so it is not a rule of thumb that Triton-derived preparations show increased inhomogeneous disorder in the red absorption bands. In fact, we have now isolated RC short preparations using a slightly different procedure that show the same degree of structure in the 4 K absorption spectrum as the RC DM-3 preparation.…”

“…Nevertheless, analysis of the spectral window of 660-690 nm yielded consistent results of all three spectra with five spectral components ( Table 2). More components will result in even better fits [see, e.g., Cattanea et al (1995)] but appeared not necessary to extract the basic features. The most important difference between RC DM-3 and RC short is the slightly larger bandwidth of the components peaking near 683 and 679 nm; the other features are virtually the same.…”

In VitroReconstitution of the Recombinant Photosystem II Light-harvesting Complex CP24 and Its Spectroscopic Characterization

“…The spectra were deconvoluted as linear combinations of symmetric Gaussians whose parameters (peak wavelength, full-width at half-maximum, and percentage amplitude to the 630 -720-nm spectrum integral) were kept free. The only constraint considered was the final control of the total bandwidth in the 9 -11-nm range, as expected from the analysis of electron-phonon coupling and site-inhomogeneous broadening in a variety of antenna chlorophyll proteins (10,12,37,38) in the accepted solutions. For the sake of model simplicity and reducing the arbitrariness of the fitting, the minimal choice of adjustable parameters was always used, i.e.…”

Photosynthesis research in Italy: a review

“…Analysis of the Reaction Center trapping efficiency as a function of the different Chl spectral pools, present in the Photosystem II antenna, revealed that a 683-684 spectral form was most strongly coupled to the Reaction Center (Jennings et al 1991b. This spectral pool was subsequently shown to be also an important component of the Reaction Center complex (Cattaneo et al 1995) and compartment modeling of Photosystem II in terms of its component chlorophyll/protein complexes shows that this determines its strong coupling to Photosystem II primary photochemistry .…”