Absorption, fluorescence, and CD spectral properties of the isolated D1/D2/cytochrome b-559 photosystem II reaction center complex were examined in stabilized reaction center material at 77 K. Spectral properties were dependent on the presence or absence of 0.05% Triton X-100 in the RC suspension medium, on the redox state of pheophytin, and on the state of inactivation of the complex. The specific spectral properties of the PS II RC complex in the red suggest that the primary donor is not a bacterial-type special pair and could be a monomer. Furthermore, the spectral properties in the PS II RC may be the result of excitonic interactions among all the porphyrin molecules in the complex. Interactions between fl-carotene and porphyrins indicate a significant role for fl-carotene in the PS II RC.

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The interrelation between spectral and structural-functional properties of LhcIIb was studied. The dipole strength of the main Q(y )bands of chlorophylls (Chl a 30.8 D(2); Chl b 18.5 D(2)) and chlorophyll a/b ratio (Chl a/Chl b = 7 : 6) were determined for LhcIIb. The Chl a/Chl b value shows that the subunit of this complex contains seven Chl a and six Chl b molecules. Individual bands of chlorophylls (bands in stokes and anti-Stokes parts at 77 K were Lorentzian and Gaussian, respectively) were resolved using synchronized deconvolution of absorption, CD, and LD bands of chlorophylls. Seven of these bands belonged to Chl a. Parameters of absorption bands of Chl a indicate that seven molecules represent a united cluster (heptamer) with exciton interactions, determining the spectrum of LhcIIb in the Chl a absorption region. Parameters of absorption bands of Chl b show the existence of three clusters: monomer (639.6 nm), dimer (645.2 and 647.4 nm), and trimer (649.8 and 654.1 nm). These clusters and their properties agree with the well-known structure of porphyrin groups of the LhcIIb subunit (Kuhlbrandt, 1994). A distorted ring of seven porphyrins in the stromal range of the subunit corresponds to Chl a heptamer; a separately located molecule near the N-terminal domain on the stromal side of the subunit corresponds to Chl b monomer; a dimer and a trimer of porphyrins in the lumenal range of the subunit correspond to the dimer and trimer of Chl b, respectively. The calculated lifetimes of the excitation energy (exciton) transfer in subunit and trimer of LhcIIb confirm this location of pigments. The geometry of the Chl a heptamer (mutual orientation of transition dipole moments) was determined by the steady-state Kasha-Tinoco approximation using parameters of individual bands of exciton splitting. The calculated parameters of mutual orientation of Chl a dipoles agree with the topography of the stromal porphyrins found by electron crystallography (Kuhlbrandt, 1994). A structural model of the granal multicentral macrocomplex of PSII (MPSII) is suggested. The lifetimes of the exciton migration between the main pigment-protein compartments of MPSII were calculated. The results of calculation are consistent with the structural model of the photosystem. The location of pigments provides for fast exciton hopping between Chl a clusters of neighboring proteins in the MPSII along the stromal surface within the membrane (5-25 psec) and between stacked membranes (approximately 40 psec) of chloroplast grana.

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