Spectral properties of stabilized D1/D2/cytochrome b-559 photosystem II reaction center complex Effects of Triton X-100, the redox state of pheophytin, and β-carotene

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 β-carotene and porphyrins indicate a significant role for β-carotene in the PS II RC.