A thermal broadening study of the antenna chlorophylls in PSI-200, LHCI, and PSI core.
The intact photosystem I of maize containing its full antenna complement (PSI-200) has been purified and fractionated into the core and outer antenna (LHCI) components. It is demonstrated by absorption and fluorescence spectroscopy that at least 80% of the long wavelength absorbing antenna pigments (red forms) are located in LHCI. Absorption spectra in the Qy region of all three preparations were measured between 72 and 300 K and subjected to a thermal broadening analysis. Data are interpreted in the linear electron-phonon coupling assumption, and the average optical reorganization energy (Snum) for the bulk pigment band and the red absorption tail determined. A marked asymmetry in Snum values across the absorption band is demonstrated. The bulk pigments in all three preparations have rather low values, in the range of 15-25 cm-1, suggesting that Stokes shifts for the absorption forms are in the 1. 5-3 nm range. On the other hand the red forms have markedly greater reorganization energies. While a direct thermal analysis of the red tail indicates minimum Snum values of around 60 cm-1, when the contribution of the red tail of the bulk pigments is corrected for in LHCI, the more reliable value of 110 cm-1 is obtained. These high Snum values for the red pigment forms suggest that they have unusually wide homogeneously broadened absorption bands and large Stokes shifts (6-11 nm).
Croce
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R
Centro C.N.R. Biologia Cellulare e Molecolare delle Piante, Dipartimento di Biologia, Università di Milano, Italy.
Zucchelli
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G
Garlaschi
F M
FM
Jennings
R C
RC
D002352:Carrier Proteins / Q000737:chemistry; D002734:Chlorophyll / Q000737:chemistry*; D002736:Chloroplasts / Q000737:chemistry; D045342:Light-Harvesting Protein Complexes; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry*; D045331:Photosystem I Protein Complex; D045332:Photosystem II Protein Complex; D010940:Plant Proteins; D013050:Spectrometry, Fluorescence; D013053:Spectrophotometry; D013696:Temperature; D013816:Thermodynamics; D003313:Zea mays
D002352:Carrier Proteins; D045342:Light-Harvesting Protein Complexes; D045322:Photosynthetic Reaction Center Complex Proteins; D045331:Photosystem I Protein Complex; D045332:Photosystem II Protein Complex; D010940:Plant Proteins; C085170:chlorophyll a-b-binding protein type II, Zea mays; D002734:Chlorophyll