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Experimental study is carried out to model the circular dichroism (CD) spectrum of LHCII, the main light harvesting antenna of photosystem II of higher plants. The findings state that differences in the experimental trimeric CD spectra are caused by changes in the strength of the monomer-monomer interactions due to the differences in detergents used for the purification of the complexes.

The spectroscopic characteristics of carotenoids associated with the antenna complexes of Photosystem I is studied. It is suggested that in the Lhca2-Lhca3 heterodimeric complex energy equilibration is not complete at least on a fast time scale.

Research has been conducted on the chlorophyll-xanthophyll-protein CP26 complex purified from leaves or recombinant. The pigment binding site affinity of this complex has been investigated via the use of the biochemical and spectroscopic analysis of the complexes in the presence of different ratios between chromophores and the details are reported.

The pigment-protein interactions in the photosystem II antenna protein, Lhcb4, reveal that removal of a any bound cofactor from any sites of the chlorophyll a binding sites, a2, a4, and a5 leads to a loss of bands of the particular chlorophyll molecule and a structural impact on the protein folding.

Results show that spectral properties and photochemical behavior of xanthophyll pigments are reflections of the individual pigments bound to the light-harvesting complexes. Data on the absorption wavelengths and fluorescence of the bound pigments are discussed.

Existence of two spectroscopically different dimers of light-harvesting complex I from green plants has been supported by recent research. A preparation of isolated dimeric peripheral antenna complexes from green plant photosystem I has been studied using low-temperature polarized steady-state absorption and fluorescence spectroscopy. The chlorophylls responsible for the 733 nm emission and the 702 nm emission are excitonically coupled dimers. F-730 comes from one of the strongest chlorophyll coupled pairs seen in nature.

Photosytem I from maize, having its full antenna complement (PSI-200) has been studied by time-resolved fluorescence methods with about 5 ps resolution at 280 and 170 K in the 690-780 nm wavelength range. Detergent effects of chlorophyll coupling were almost entirely lacking in the preparation from maize. Decay-associated spectra (DAS) data and the time-resolved emission spectra (TRES) data were developed. The data show that trapping in PSI-200 is to a great extent rate-limited by excitation diffusion in the antenna and especially by the gradual 'uphill' transfer from the low-energy forms to the bulk and/or inner core chlorophyll molecules

The thermal broadening of the red absorption tail of the full antenna complement (PSI-200), core and outer antenna (LHCI) and PSI core of the intact photosystem I of maize was investigated in terms of the second-order central moment and compared with that of the bulk antenna pigments. Results of absorption and fluorescence spectroscopic studies showed that at least 80% of the long wavelength absorbing antenna pigments are found in LHCI. The bulk pigments in all three preparations were found to have low values, indicating that Stokes shifts for the absorption forms are in the 1.5-3 nm range.

Thermodynamic analysis of adsorption and fluorescence spectra of the in vitro reconstitution of the photosystem II antenna complex CP29(Lhcb-4) and of modulation of pigment constitution during reconstitution found that all chlorophylls (chl) are energetically connected. Data indicate that most chl sites can bind either chl a or chl b. The invariant position of chl a dn chlb adsorption bands with changing chla/chlb binding stoichiometries suggests that pigment-protein interactions are the main determinants of spectral heterogeneity.

The organization of chl molecules in the membrane plane is affected by the reversible phophorylation of the hydrophilic N-terminal domain of CP29 due to long range allosteric effects. The addition of alkaline phosphatase reverses the variations in the organization of chlorophyll chromatophores of phosphorylated and unphosphorylated forms of CP29. Long-range conformational changes due to phosphorylation are responsible for the variations in the structure of CP29.

The primary donor P700 of photosystem I (PSI) is isoenergetic with its antenna at room temperature. The free energy for excitation transfer from the antenna to P700 is -0.26 kT at room temperature. Fluorescence analysis of PSI between 75 and 280 kelvin with its full antenna complement reveals the presence of a minimum of three chlorophyll spectral forms. The emission maxima of the spectral forms are 720, 730 and 742 nm respectively. At least three or four antenna chlorophylls with absorptions of about 695 nm are linked to P700.

The biochemical and spectroscopic properties of the three groups of genes encoding LHCII components namely Lhcb1, Lhcb2 and Lhcb3 are analyzed. The Lhcb2 pigment-protein shows different spectroscopic properties with respect to Lhcb1 and the hypothesis is suggested that Lhcb3 may be a preferential site of regulation of the antenna function in excess light conditions.

Research demonstrates the biosynthesis of Arabidopsis thaliana recombinant photosystem I antenna complexes, Lhca2 and Lhca3, in Escherichia coli and reconstitution of the pigment-refolded protein complexes. Data reveal that the complexes can modulate the absorption/emission properties and red-shifted spectral characteristics of the native forms.

Research was conducted to examine the orientation of the Q(sub y) transition of the individual chlorophyll (Chl) molecules in the higher-plant antenna protein CP29. Low-temperature linear dichroism and absorption spectroscopy were used to investigate the single-point mutants. Results permit the determination of the orientation of six chromophores within the protein structure. The orientation of the dipole moments of two Chl molecules indicate a role in energy transfer from xanthophyll to Chl.