Resonance Raman spectroscopy of carotenoids in Photosystem II core complexes

Resonance Raman (RR) spectroscopy has been used to examine the configuration of the carotenoids bound to Synechocystis PCC 6803 Photosystem II (PS II) core complexes. The excitation wavelengths used (514.5, 488.0, 476.5 and 457.9 nm) span the absorption bands of all of the ~12–17 neutral carotenoids in the PS II core complex. The RR spectra of the two carotenoids associated with the D1–D2 polypeptides (Car 507 and Car 489 ) of the reaction center are extracted via light versus dark difference experiments measured at 20 K. The RR results are consistent with all- trans configurations for both Car 507 and Car 489 and indicate that majority of the other carotenoids in the PS II core complex must also be in the all- trans configuration. The configuration of β-carotene is relevant to its proposed function as a molecular wire in the secondary electron-transfer reactions of PS II.